Device and method for controlling energy

ABSTRACT

Apparatuses and methods for applying EM energy to a load. The apparatuses and methods may include at least one processor configured to receive information indicative of energy dissipated by the load for each of a plurality of modulation space elements. The processor may also be configured to associate each of the plurality of modulation space elements with a corresponding time duration of power application, based on the received information. The processor may be further configured to regulate energy applied to the load such that for each of the plurality of modulation space elements, power is applied to the load at the corresponding time duration of power application.

RELATED APPLICATIONS

This is a continuation of application Ser. No. 13/508,940, filed May 9,2012, which claims the benefit of 1) International Application No.PCT/IL2010/000380 entitled “Device and Method For Controlling Energy,”filed on May 12, 2010; 2) International Application No.PCT/IL2009/001057 entitled “Device and Method For Controlling Energy,”filed on Nov. 10, 2009; 3) U.S. Provisional Patent Application No.61/282,981, entitled “Modal Analysis,” filed on May 3, 2010; 4) U.S.Provisional Patent Application No. 61/282,983, entitled “Loss ProfileAnalysis,” filed on May 3, 2010; and 5) U.S. Provisional PatentApplication No. 61/282,980, entitled “Spatially Controlled EnergyDelivery,” filed on May 3, 2010. All of these listed applications arefully incorporated herein by reference in their entirety.

The present application is related to four other U.S. Provisional PatentApplications 1) U.S. Provisional Application No. 61/282,985, entitled“Modal Energy Application,” filed on May 3, 2010; 2) U.S. ProvisionalApplication No. 61/282,986, entitled “Degenerate Modal Cavity,” filed onMay 3, 2010; 3) U.S. Provisional Application No. 61/282,982, entitle“Partitioned Cavity,” filed on May 3, 2010; and 4) U.S. ProvisionalApplication No. 61/282,984, entitled “Antenna Placement in anElectromagnetic Energy Transfer System,” filed on May 3, 2010. All ofthese listed applications are fully incorporated herein by reference intheir entirety.

FIELD OF THE INVENTION

The present application, in some embodiments thereof, is concernedgenerally with dissipation of electromagnetic (EM) energy in a load, andmore particularly but not exclusively with RF heating, for example usingmicrowave or UHF energy for thawing, heating and/or and cooking.

BACKGROUND OF THE INVENTION

Heating objects using high frequency radiation is wide spread, andcomprises the commonly used domestic microwave (MW) oven, as well ascommercial ovens that use MW energy, mainly in combination with othermeans of heating, such as steam, hot air and infrared heating elements.

Among the many problems associated with known MW ovens is a lack ofuniformity in heating, which often results in hot spots and cold spotsthat reflect the standing wave within the cavity. Many of the attemptsto improve uniformity in such devices included increasing the number ofmodes within the cavity (e.g. by mode stirring and/or moving the loadduring heating).

In some cases, where multiple frequencies were used, the devices wereconfigured to measure the efficiency of energy transfer into the cavityat different transmitted frequencies and then to transmit energy to theload only at frequencies having a relatively high efficiency, with theintent that this should increase the efficiency of energy transfer intothe load.

Heating an object changes its dissipation characteristics at differentfrequencies. For example, a frequency that is dissipated in the load atone rate before heating may dissipate at a different rate (higher orlower) after some heating or movement of the load took place.

SUMMARY OF THE INVENTION

According to some embodiments there is provided an apparatus and amethod for irradiating a load with an irradiation spectrum offrequencies. Irradiating is performed by transmitting different amountsof energy at different frequencies. The amount of energy transmitted ateach frequency is controlled by at least by varying respective durationsduring which corresponding frequencies are transmitted.

According to one aspect of the present embodiments, a method ofirradiating a load is provided in which different amounts of energy aresupplied at different frequencies by varying the respective durationsduring which corresponding frequencies are transmitted. Hence afrequency which from which much energy is required is transmitted for alonger amount of time and a frequency from which little energy isrequired is transmitted for a shorter amount of time.

Irradiating the load may be performed in a resonance cavity.

Irradiating the load may be controlled for obtaining a predeterminedenergy dissipation pattern in the load.

Irradiating the load may be performed at a fixed power transmissionlevel.

Irradiating the load may be performed at a maximal power transmissionlevel for each of the transmitted frequencies respectively. Keeping theamplifier working at a design maximum power allows for cheaperamplifiers to be used.

Irradiating the load may be controlled for limiting the maximum amountof energy provided at each of the different frequencies.

Irradiating the load may be controlled for limiting the overall amountof energy provided at the different frequencies for a period oftransmission.

A period of transmission may be a transmission cycle or a duty cycle.

Irradiating the load may be controlled for limiting the overalldurations during which individual frequencies are transmitted.

Irradiating the load may be controlled for maximizing the possible powerat each of the transmitted frequencies.

At least two frequencies are transmitted at at least two differentnon-zero powers.

The method may comprise:

irradiating the load with the irradiation spectrum of frequencies;

measuring a resulting reflected and coupled spectrum (RC spectrum);

inferring current dissipation information of the load in view of the RCspectrum; and

setting the irradiation spectrum of frequencies to accord with thedissipation information wherein the setting comprises transmittingdifferent amounts of energy at different frequencies by varyingrespective durations during which corresponding frequencies aretransmitted.

The method may comprise:

irradiating the load with the irradiation spectrum of frequencies, suchthat energy is absorbed by the load;

measuring a resulting RC spectrum;

inferring current dissipation information of the load in view of themeasured RC spectrum; and

modifying the irradiation spectrum of frequencies to accord with thedissipation information wherein the modifying comprises transmittingdifferent amounts of energy at different frequencies by varyingrespective durations during which corresponding frequencies aretransmitted.

The frequencies may be arranged in a series to form a duty cycle.

The method may comprise repetitively performing the duty cycle.

The frequencies are varied within the duty cycle.

The method may comprise switching frequencies differentially on or offover repetitions of the duty cycle to vary overall durations ofirradiation at respective frequencies of irradiation of the load.

In the method, differential switching may be achieved by switching afrequency off for some of the cycles or to a lower power for some of thecycles.

According to a second aspect of the present embodiments there isprovided a method for irradiating a load with an irradiation spectrum offrequencies, the load having dissipation information which varies as afunction of an energy dissipation state of the load, the methodcomprising modifying the irradiation spectrum of frequencies to accordwith the varying of the dissipation information wherein the modifyingcomprises varying respective durations during which correspondingfrequencies are transmitted.

According to a third aspect of the present embodiments there is providedapparatus for irradiating a load, comprising:

a. an energy feed functional for transmitting energy to a cavity forresonating in the presence of the load in a plurality of frequencies;and

b. a controller functional for varying respective durations during whichcorresponding frequencies are transmitted.

In an embodiment, the controller is configured to carry out the varyingrepeatedly.

In an embodiment, the controller is configured to irradiate the loadwith the irradiation spectrum of frequencies according to the respectivedurations, to measure a resulting reflected and coupled spectrum (RCspectrum), to infer current dissipation information of the load in viewof the RC spectrum, and to set the irradiation spectrum of frequenciesto accord with the dissipation information.

In an embodiment, the controller is configured to switch frequenciesdifferentially on or off over repetitions of a duty cycle of thefrequencies, thereby to vary overall duration of respective frequenciesin the irradiating the load.

Some exemplary embodiments may include an apparatus for applying EMenergy to a load. The apparatus may include at least one processorconfigured to receive information indicative of energy dissipated by theload for each of a plurality of modulation space elements, a term to bedescribed in greater detail below. The processor may also be configuredto associate each of the plurality of modulation space elements withcorresponding time duration of power application, based on the receivedinformation. The processor may be further configured to regulate energyapplied to the load such that for each of the plurality of modulationspace elements, power is applied to the load at the corresponding timeduration of power application.

Other exemplary embodiments may include an apparatus for applying EMenergy to a load. The apparatus may include at least one processorconfigured to determine a plurality of values of dissipation indicatorsassociated with the load. The processor may also be configured to setmodulation space element/power/time triplets based on the plurality ofvalues of dissipation indicators. The processor may further beconfigured to regulate application of the modulation spaceelement/power/time triplets to apply energy to the load.

Other exemplary embodiments may include a method for applying EM energyto a load. The method may include receiving information indicative ofenergy dissipated by the load for each of a plurality of modulationspace elements; associating each of the plurality of modulation spaceelements with a corresponding time duration of power application, basedon the received information; and regulating energy applied to the loadsuch that for each of the plurality of modulation space elements, poweris applied to the load at the corresponding time duration of powerapplication.

In the present disclosure, many of the concepts have been described inconjunction with frequencies and/or modulation space elements. In someembodiments, frequency may be included among one or more parameters usedto define or manipulate a modulation space element. In general,therefore, concepts relating to the presently disclosed embodiments thatare described in terms of frequency may also extend more generally toembodiments that include the use of modulation space elements.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. The materials, methods, andexamples provided herein are illustrative only and not intended to belimiting.

The word “exemplary” is used herein to mean “serving as an example,instance or illustration”. Any embodiment described as “exemplary” isnot necessarily to be construed as preferred or advantageous over otherembodiments and/or to exclude the incorporation of features from otherembodiments.

The word “optionally” is used herein to mean “is provided in someembodiments and not provided in other embodiments”. Any particularembodiment of the invention may include a plurality of “optional”features unless such features conflict.

Implementation of the method and/or system of embodiments of theinvention can involve performing or completing selected tasks manually,automatically, or a combination thereof. This refers in particular totasks involving the control of the equipment such as a microwave, dryerand the like. Moreover, according to actual instrumentation andequipment of embodiments of the method and/or system of the invention,several selected tasks could be implemented by hardware, by software orby firmware or by a combination thereof using an operating system.

For example, hardware for performing selected tasks according toembodiments of the invention could be implemented as a chip or acircuit. As software, selected tasks according to embodiments of theinvention could be implemented as a plurality of software instructionsbeing executed by a computer using any suitable operating system. In anexemplary embodiment of the invention, one or more tasks according toexemplary embodiments of method and/or system as described herein areperformed by a data processor, such as a computing platform forexecuting a plurality of instructions. Optionally, the data processorincludes a volatile memory for storing instructions and/or data and/or anon-volatile storage, for example, a magnetic hard-disk and/or removablemedia, for storing instructions and/or data. Optionally, a networkconnection is provided as well. A display and/or a user input devicesuch as a keyboard or mouse are optionally provided as well.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings. With specific reference now tothe drawings in detail, it is stressed that the particulars shown are byway of example and for purposes of illustrative discussion of thepreferred embodiments of the present invention only, and are presentedin order to provide what is believed to be the most useful and readilyunderstood description of the principles and conceptual aspects of theinvention. In this regard, no attempt is made to show structural detailsof the invention in more detail than is necessary for a fundamentalunderstanding of the invention, the description taken with the drawingsmaking apparent to those skilled in the art how the several forms of theinvention may be embodied in practice.

In the drawings:

FIG. 1A is a simplified flow chart illustrating a method for ofirradiating a load according to some embodiments of the presentinvention.

FIG. 1B is a simplified flow chart illustrating a method according tosome embodiments of the present invention for providing controlledenergy irradiation to a load whose dissipation information variesdepending on the energy state of the load.

FIG. 1C is a simplified flow chart of a method of controlling the amountof energy that dissipates into a load at each transmitted frequencythrough modulation of the period in which each frequency is transmittedaccordance with some embodiments of the invention.

FIG. 2 is an exemplary flow chart of controlling the transfer of energyby irradiation in a plurality of frequencies.

FIG. 3 schematically depicts a device in accordance with an exemplaryembodiment of the present invention.

FIGS. 4A and 4B depict schematic graphs of power versus frequency for anexemplary decision functions.

FIG. 5 is an exemplary scenario of controlling a duty cycle forirradiating a load, according to embodiments of the present invention.

FIG. 6 is a diagram of an apparatus for applying electromagnetic energyto an object, in accordance with an exemplary embodiment of the presentinvention;

FIG. 7 illustrates a dissipation ratio spectrum (dashed line) and aninput energy spectrum (solid line), in accordance with an embodiment ofthe invention;

FIG. 8 illustrates a dissipation ratio spectrum, in accordance with anembodiment of the invention;

FIG. 9 represents a device in accordance with an exemplary embodiment ofthe present invention; and

FIG. 10 illustrates an exemplary modulation space.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present embodiments comprise an apparatus and a method forcontrolling the amount of EM energy that dissipates into a load at eachtransmitted modulation space element (MSE; as will be described below indetail) and in particular, to such a controlling through modulation ofthe period in which each MSE is transmitted, particularly within a dutycycle of the MSEs. The dissipation of energy may be used, for example,for any form of heating utilizing irradiation of energy, at timeswithout a temperature increase, including one or more of thawing,defrosting, warming, cooking, drying etc. The term “electromagneticenergy” or “EM energy”, as used herein, includes any or all portions ofthe electromagnetic spectrum, including but not limited to, radiofrequency (RF), infrared (IR), near infrared, visible light,ultraviolet, etc. In one particular example, applied electromagneticenergy may include RF energy with a wavelength in free space of 100 kmto 1 mm, which is a frequency of 3 KHz to 300 GHz, respectively. In someother examples, the frequency bands may be between 500 MHz to 1500 MHzor between 700 MHz to 1200 MHz or between 800 Mhz-1 GHz. Microwave andultra high frequency (UHF) energy, for example, are both within the RFrange. Even though examples of the invention are described herein inconnection with the application of RF energy, these descriptions areprovided to illustrate a few exemplary principles of the invention, andare not intended to limit the invention to any particular portion of theelectromagnetic spectrum.

PCT patent applications No WO2007/096877 ('877) and WO2007/096878('878), both by Ben-Shmuel et al. (both published on Aug. 3, 2007)herein incorporated by reference, disclose methods and devices forelectromagnetic heating. Some disclosed methods comprise the steps ofplacing an object to be heated into a cavity and feeding UHF ormicrowave energy into the cavity via a plurality of feeds and at aplurality of frequencies.

PCT patent application No WO2008/102,360 ('360) by Ben Shmuel et al,published on Aug. 28, 2008, herein incorporated by reference, discloses,inter alia, a method for drying an object comprising applying broadbandRF energy to an object in a cavity, in a controlled manner which keepsthe object within a desired temporal temperature schedule and within adesired spatial profile; and terminating the drying when it is at leastestimated that a desired drying level is achieved.

PCT patent application No WO2008/102,334 ('334) by Ben Shmuel et al,published on Aug. 28, 2008, herein incorporated by reference, discloses,inter alia, a method for freezing a body or a portion of a body. Themethod comprises exposing at least a part of the body to a coolanthaving a temperature below the freezing point of the body, and at thesame time operating an electromagnetic heater, as to maintain the atleast part of the body at a temperature above its freezing point; andreducing the electromagnetic heating to allow the at least a part of thebody to freeze. The electromagnetic heater comprises a resonator, andthe heated part of the body is heated inside the resonator.

The aforementioned methods of the '877, '878 and '334 applications takeinto account the dissipation ratio at each transmitted frequency and themaximal amount of power that may be transmitted at that frequency. Themethods aim, at times, to deduce the amount of energy that is to betransmitted at each frequency such that only a desired amount of energyis dissipated.

The aforementioned methods of the '877, '878 and '334 applicationsfurther disclose the option of transmitting power only (or primarily) inbands that primarily dissipate in the load. Such transmission may beused, for example, to avoid or significantly reduce dissipation intosurface currents or between multiple feeds (i.e., antennas). Thetransmission can be performed, for example, such that the powerdissipated in the object is substantially constant for all transmittedfrequencies (which may be termed a homogeneous energy dissipationpattern in the load). Such a transmission allows an essentially equaldissipation of energy per frequency in the load, regardless of theload's composition and/or geometry, while the power fed and efficiencyof energy transfer may be different for different frequencies.

According to some embodiments of the present invention, a method isprovided for irradiating a load with a spectrum of frequencies or MSEs,measuring a resulting reflected and coupled spectrum (“RC spectrum”),inferring from the RC spectrum the spectral dissipation of the load asit is modified over the course of the irradiation, and modifying theirradiation spectrum in response to the changing dissipation spectrum.“Spectral dissipation” or “dissipation information” of a load may betaken to mean the dissipation ratios of a plurality of transmittedfrequencies or MSEs in the load.

Alternatively or additionally, modifying the irradiation is performed bydynamically adjusting one or more parameters for controlling the amountof energy that dissipates into a load at each transmitted frequency in aduty cycle. The adjustment is based on spectral information retrievedfrom the load. Spectral information may comprise and/or be derived fromone or more of the RC spectrum the full S parameters of the device, thespectral dissipation of the load, the dissipation ratios of transmittedfrequencies or MSEs in the load, the Q factor associated withdissipation peaks, and/or the maximal power that may be transmitted intothe cavity at each such frequency or MSE). Such parameters forcontrolling the heating may be or include the time allotted per eachfrequency and/or the power assigned for each frequency and the like.

According to some embodiments of the present invention the transmittaltime for each frequency or MSE is adjusted such that a desired energy isdissipated into the load at any given frequency or MSE. In such aprotocol, the time of transmission may be used to compensate for caseshaving a relatively low energy dissipation ratio and/or low maximalpower input by assigning more time for such frequencies or MSEs (e.g. ifa high relative energy transmission is desired for such frequencies in agiven cycle). The energy that is dissipated in a load at a givenfrequency or MSE may be controlled to achieve a desired dissipationpattern in the load. Accordingly, the desired energy may be, forexample, an absolute value per frequency or MSE or a relative value (ascompared to another transmitted frequency or MSE) or a combination ofboth. It may also be related to the total amount of energy that shouldbe dissipated in a plurality of frequencies or MSEs and the pattern(relative dissipation ratio) between them. A dissipation pattern in theload means the relative and/or absolute amount of energy that needs tobe dissipated in a load that is exposed to irradiation at each frequencyor a plurality of frequencies or MSEs. The pattern may be frequency orMSE related (e.g., dissipate a given or relative amount by a frequencyor MSE) and/or site related (e.g., dissipate a given or relative amountinto a site in the load) or another parameter or characteristic of thespectral information (possibly across the whole working band). Forexample—a dissipation pattern may be homogeneous (essentially the sameamount of energy to be dissipated by a plurality of frequencies or MSEsand/or at a plurality of sites). For example, for homogeneous energydissipation, all, or a significant majority (e.g. 51% or more, 60% ormore, 80% or more, or even 95% or more), of the dissipated energy valuesfor each frequency in a heating cycle must be similar (e.g., maximumdifference lower than 40%, 20%, 10%, 5% of the mean value). In otherpatterns, a different relation may exist. For example, in some protocolsthat may be used for thawing, a relatively small amount of energy (ifany) may be dissipated in the load for frequencies or MSEs having a highdissipation ratio, while a relatively large amount of energy may bedissipated in the load for frequencies or MSEs having a low dissipationratio. An energy dissipation pattern may comprise one or more of (a)homogeneous energy dissipation in the load, (b) controlled,non-homogeneous energy dissipation in the load or (c) a combinationthereof. The dissipation pattern may be chosen per irradiation cycle orit may be chosen for a plurality of cycles or even the whole process.

A time adjusted method may enable a reduction in the overall processtime in comparison to adjusting only the power input at each frequencyor MSE (e.g., where the transmission time per frequency or MSE is fixed)since a higher power level (at least in some frequencies or MSEs)becomes possible. Optionally, highest power level (as a function offrequency or MSE) is transmitted at all frequencies or MSEs, maximizing(for given spectral situation and power source) the energy dissipationratio, thus minimizing the time. The controlling of the time may beperformed one or more times during heating, for example, before eachduty cycle, and/or before and/or after a plurality of duty cycles, andmay be based on spectral information or dissipation informationretrieved from the cavity and/or the load. The control may encompass,for example, the control of the device over the different frequencies orMSEs to ensure that each frequency or MSE is transmitted at a power andduration as necessary. At times, control may also encompass the changeof transmission patterns, for example, between cycles and, at times,also respective calculations and/or decision making processes.

Additionally, or alternatively, the maximal possible power at eachtransmitted frequency or MSE is transmitted for that frequency or MSE,while controlling the time period of transmission for that frequency orMSE. Such transmission results in dissipating a desired amount of energyat the given frequency or MSE into the load. Such transmission resultsin an increase or even maximization of the dissipated power (or rate ofenergy transfer to the load) while achieving a desired energydissipation pattern. Additionally or alternatively a reduction or evenminimization of the time needed for dissipating any given amount ofenergy using a given energy dissipation pattern is achieved.Surprisingly, energy transfer at the maximal possible power at carefullychosen frequencies or MSEs over the spectrum does not cause damage tothe object, although the transfer of energy at one frequency or MSE mayaffect the load's dissipation of a consequently transmitted frequency orMSE.

According to some embodiments of the present invention, the timeallotted for transmission of each frequency or MSE is fixed for alltransmitted frequencies or MSEs within a duty cycle while thefrequencies or MSEs that appear in each cycle are dynamically selected,so that summation over many cycles may provide a desired dissipationpattern, according to spectral information and/or dissipationinformation retrieved from the cavity and/or load. The embodiment isexplained in greater detail in FIG. 5 and its associated description.

According to some embodiments of the present invention, the timeallotted for transmission of each frequency or MSE may be fixed for alltransmitted frequencies or MSEs within a duty cycle while the power isdynamically adjusted over a series of duty cycles so that a desiredheating pattern is achieved over the series of cycles (a preset group ofcycles). In such cases, it may be possible to transmit each frequencyrepeated cycle within the group of cycles, until the desired energy isdissipated by that frequency or MSE. The transmission power for eachfrequency or MSE may be maximal for at least a portion of the cycleswithin the group of cycles, such that a desired amount of energy isdissipated in total by the frequency or MSE. At times, this means thatthe frequency or MSE may be transmitted at maximal power during some ofthe cycles within a group and at a lower power (or even not at all) forone or more cycles within a group. The controlling of the power may bebased on spectral information and/or dissipation information retrievedfrom the cavity and/or load.

The principles and operation of an apparatus and method according to thepresent invention may be better understood with reference to thedrawings and accompanying description.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not limited in its applicationto the details of construction and the arrangement of the components setforth in the following description or illustrated in the drawings. Theinvention is capable of other embodiments or of being practiced orcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting.

FIG. 1A is a simplified diagram illustrating a first embodimentaccording to the present invention of a method for irradiating a loadover a sequence of frequencies. According to some embodiments of thepresent invention, there is provided a method in which the transmittaltime for each frequency in a sequence of transmitted frequencies isadjusted such that a desired energy is dissipated into the object atthat given frequency. The amount of time for transmission of eachfrequency may be deduced (and accordingly controlled) each time thespectral information and/or dissipation information is updated or ateach duty cycle or for several duty cycles or even during a duty cycle,based on spectral information and/or dissipation information. Referenceis now made to box 2, in which frequencies to be transmitted to a loadare provided. The frequencies are, at times, predetermined although moregenerally they may be selected dynamically during the irradiationprocess (e.g., based on spectral information and/or dissipationinformation). In box 4, the transmission duration per each selectedfrequency is determined. The transmittal time for each frequency isadjusted such that a desired energy (absolute or relative) is dissipatedinto the object at any given frequency in a given cycle (or plurality ofcycles). In box 6, the load is irradiated such that each frequency fromthe selected frequencies is transmitted for the duration that was set inbox 2.

Reference is now made to FIG. 1B, which is a simplified flow chartillustrating a method for providing controlled energy irradiation to aload according some embodiments of the present invention andillustrating how feedback from the load and/or cavity can be used forsetting of the transmission times for the various frequencies. Normallya load has an energy dissipation characteristic which is not static butrather varies depending on a current state of the load.

More generally, differing materials (or materials having varyingcharacteristics) typically have variable absorptive properties (e.g. dueto being composes of a plurality of materials or of a material havingdifferent phases). Moreover, absorptive properties are often a functionof temperature and/or phase of the materials in the object. Thus, as thetemperature and/or phase of an object changes, the object's absorptiveproperties may change, and the rate and magnitude of this change maydepend on properties of material(s) in the object. In addition, theshape of an object may contribute to its absorptive properties at aparticular frequency. Irregularly shaped objects, for example, mayexhibit irregular electromagnetic energy absorption. All these factorscan make it difficult to control the absorption of electromagneticenergy in an object.

In box 32, the cavity is irradiated with the irradiation spectrum offrequencies. In box 34, a resulting RC spectrum is measured. The stepsshown in boxes 32 and 34 may be performed such that the measurementitself would not transmit a significant amount of energy to the load.This may be done for example at a low power that would have little or noheating effect, but would suffice for obtaining the reflectancespectrum. Alternatively the spectral information (or dissipationinformation) may be measured by transmitting at high power, but for avery short time (e.g. 1, 10, 100 or even 1000 msec). The reflectancespectrum indicates, inter alia, the dissipation information orcharacteristics for each transmitted frequency and for the wholetransmitted spectrum. In box 36 a current dissipation information of theload is inferred.

In box 38, the irradiation spectrum of frequencies is set to accord withthe dissipation information inferred in previous steps. This setting mayinclude setting the selection of which frequencies to transmit and/orsetting a transmission power and/or time to accord with the dissipationinformation, and may include the necessary calculation steps needed toset such parameters based on the dissipation information. When allfrequencies are transmitted for the duration that is set for them, oneduty cycle is finished and a new cycle may commence. Such a duty cyclemay be deemed to include a plurality of transmission cycles.

Thereafter, the irradiating in box 38 may be stopped and the process maybe repeated (boxes 32-38), thereby dynamically resetting thetransmission times to accord with the changes in the RC spectrum (ordissipation spectrum) during heating. Thus the load may be irradiatedsuch that a wanted dissipation pattern is achieved. Relative amounts ofenergy transmitted at different frequencies may be adjusted in responseto the respective dissipation ratios at each frequency in the band.Alternatively, the relative amounts of energy transmitted may beadjusted in response to a function or derivation of the dissipationratios at all the frequencies in the band, thereby affecting the energydistribution pattern in the load.

Reference is now made to FIG. 1C, which is a simplified flow chart of amethod of controlling the amount of energy that dissipates into a loadat each transmitted frequency through modulation of the period in whicheach frequency is transmitted. In box 42, the load is irradiated by UHFor Microwave radiation, using a sequence of frequencies in a duty cycle.This may be done at relatively low power and/or at a high power for avery short transmission time such that information is obtained with verylittle energy transfer (hence little or no effect on the dissipationinformation). In box 44, dissipation information is obtained from theload. In box 46, energy levels are selected for each frequency baseddesired energy transmission pattern. This may be based for example onrespective dissipation levels and overall desired energy dissipation forthe load. In box 48, the duty cycle is set at least by selectingrespective durations within the duty cycle during which correspondingfrequencies are transmitted. Typically the given power is the maximalpossible power at that frequency, and in view of the dissipation ratiofor that frequency, the set amount of energy is transmitted. In box 49,the load is irradiated according to the duty cycle. This may be followedagain by box 42 of a new round of duty cycle modification. The initialenergy dissipation information (or in fact the whole dissipationpattern) may be obtained from pre-defined energy dissipationinformation, (e.g., expected dissipation information for an egg, or forheating water based on previous operation of the device or a like devicewith a similar load). The duty cycle is modified by varying at least therespective durations within the duty cycle during which correspondingfrequencies are transmitted. The duty cycle may comprise the frequenciesthat are used for irradiating the load and the power that is transmittedat corresponding frequencies. The energy per frequency may be limitedwithin the cycles. The limiting may be based on a maximum cumulativetime power combination for each frequency allowed for performing thecycles or on a maximum energy per frequency allowed.

As has been noted elsewhere herein, not all energy transmitted isactually dissipated (or absorbed) by the load. The proportion of energytransmitted that is absorbed by the load normally varies for differentfrequencies and for different loads. Excess transmitted energy may bereflected back to the feed or coupled to another feed if such ispresent.

FIG. 2 is an exemplary flow chart depicting control over the amount ofenergy that is transmitted. In box 21, an energy dissipation pattern isoptionally selected. In box 22, dissipation information is acquired fromthe load (e.g., by transmitting a low energy frequency sweep asdescribed above). In box 23, the dissipation information is analyzed. Inbox 24, per each frequency that is to be transmitted,frequency/time/power (FTP) triplets are selected to perform the selectedprofile. A method for selecting the triplets is explained in greaterdetail hereinafter. One or more of the FTP triplets may be fixed for allor a plurality of frequencies. In box 25 energy is transmitted to theload according to the FTP triplets. The process described in boxes 21-25may be repeated with or without new information acquisition and analysissteps. Box 26 describes the termination, which may be automatic.Automatic termination may be after a set amount of energy was dissipatedor after a given time is expired, or based on sensed input which may behumidity/temperature/volume/phase change and the like. The terminationcan also be manual.

The amount of power that is desired to be dissipated in the load at agiven frequency for a given dissipation ratio for a unit time is definedhereinafter as dpl(f). Power means the energy dissipated per unit time.Supplying different amounts of energy for different frequencies may becarried out for example by using different peak powers, different dutycycles and/or transmitting at different rates. For example, power may besupplied at fixed amplitudes, but at a different rate and/or delaysbetween pulses for different frequencies.

In power adjusted heating, the time allotted for transmission of eachfrequency is fixed for all transmitted frequencies within a cycle, butthe power may vary between frequencies. When it is desired to have ahomogeneous dissipation of power at all frequencies (or a particularrange of frequencies), dpl(f) is selected to be the same for alltransmitted frequencies. In such cases, a different power is transmittedat different frequencies having different dissipation ratios to affectan essentially homogeneous amount of energy dissipated at the respectivefrequencies.

The maximal amount of power that may be dissipated in a load in a unitof time (using a given power source—e.g. RF power amplifier) is definedas ep(f), which is a function of the dissipation ratio at that frequency(dr(f)) and the maximum power available from the power source at thatfrequency (P_(max)). Since (in power adjusted heating) the time allottedfor transmission of each frequency is fixed for all transmittedfrequencies, for some frequencies it might not be possible to dissipatea high desired amount of energy within the time slot (i.e. whereep(f)<dpl(f)). Choosing a low dpl(f) may increase the number offrequencies that can have the desired amount of power (dpl) dissipatedin them (ep(f)≧dpl(f)), and consequently the desired amount of energydissipates in more portions of the load. However, this would be at theexpense of the speed of energy dissipation. Choosing a higher dpl mayincrease the speed of heating since more energy is dissipated within agiven time slot, but also causes a higher deviation of the actual energydissipation from the selected energy dissipation pattern because morefrequencies have ep(f)<dpl and hence may receive only the maximumavailable energy, which, for those frequencies in that circumstance, islower than dpl. It is noted, that by modifying a characteristic of thecavity (e.g., by moving a field adjusting element and/or moving theload), the spectral information and/or dissipation information may bemodified such that, for example, a given dpl(f) would be transmittableat a greater number of frequencies, thereby allowing an increase of theheating rate at a given level of uniformity.

In time adjusted heating, the time allotted for transmission of eachfrequency may be varied between transmitted frequencies within a cycleand optionally the transmission power may also vary between frequencies.When it is desired to have a homogeneous, or essentially homogeneous,dissipation of power at all or some frequencies, dpl(f) is selected tobe the same for all transmitted frequencies. By using this method, adifferent time may be used to transmit at different frequencies at thesame and/or different transmission powers, but due to differentdissipation ratios, essentially the same amount of power is dissipatedin the load.

Since in time adjusted heating, the time allotted for transmission ofeach frequency may vary, e.g., in order to compensate for differences inep(f), more frequencies may be useful at a given dpl(f) than in poweradjusted heating. In fact, in time adjusted heating, the dissipationpatterns and time are virtually unlimited when compared to thoseachievable under similar conditions with power adjusted heating. Stillother limitations may be imposed, as detailed for example below, thatmight prevent the use of frequencies having too high or too lowdissipation ratios and/or ep(f). Therefore, modifying a characteristicof the cavity, for example by moving a field adjusting element and/ormoving the load, in a time adjusted protocol may also be used to modifythe number (or proportion) of frequencies which may be used to affect adesired dissipation pattern.

According to some embodiments, a desired total amount of energy to bedissipated in the load in any given transmission cycle may be set inadvance. A transmission cycle, termed also as duty cycle, is a set oftransmissions comprising all frequencies used in a working band andtransmitted at one time or in a sequence, according to a desired energydissipation pattern. In a cycle, a frequency may be transmitted once ormore than once, as with the above mentioned group of cycles, to affectthe energy dissipation pattern. A cycle, for example, can be implementedas a frequency sweep, where each frequency is transmitted once, and/oras a pulse where a plurality of frequencies are transmitted at the sametime or using and/or any other method known in the art. A cycle may bethe total transmissions of energy between resetting events of thetransmission spectrum parameters. A single heating protocol may beperformed as a single transmission cycle (especially when the desiredenergy dissipation is small) or as a plurality of transmission cycles.

According to some embodiments for time adjusted heating, a bottomtransmitted power limit may be selected, for example, to prevent anundue elongation of the cycle by the need to transmit at relatively lowep(f) (e.g., 50% or less, 20% or less, 10% or less, or even 3% or lessof the maximum ep(f) value), or when ep(f) is below a pre-set absolutevalue. This power limitation is termed herein as bpl. tpl(f)) denotesthe power that may be transmitted by the device at a given frequency todissipate dpl. Hence, tpl(f) is a function of dpl, the maximum amount ofpower that can be transmitted by the device at a given frequency and thedissipation ratio (dr(f)) at that frequency). Where tpl(f) is lower, thetime needed in order to have dpl(f) dissipated is longer than if tpl(f)was higher (for the same dpl(f)). Where tpl(f)<bpl the heating protocolmay hence be adjusted to limit the amount of time spent at suchfrequencies. For example—frequencies having a tpl(f) that is below bplmay be ignored, in other words not transmitted at all, or alternatively,they may be transmitted for a limited period of time. Thus, for example,the period of heating for ep(f)=bpl.

According to some embodiments, the amount of maximal transmitted poweris limited, for example in order to prevent damage to the device. Thelimitation is performed by setting a maximum limit on tpl(f). Thislimitation may have greater importance at low dissipation ratiofrequencies where the portion of transmitted power that is notdissipated in the load is large. The effect of this limitation may bereduced by adding protective measures to different parts of the device,such as cooling means to the reflected power load. The controller may beconfigured to prevent the power that is dissipated in the reflectedpower load from exceeding a predefined upper limit. Such a configurationmay be achieved by calculating the return and coupled energy or bymeasuring temperature or any other means known in the art.

According to some embodiments, an upper limit may be imposed on thepower level that is allowed to be transmitted into the cavity for anyreason, including for example prevention of damage to the device andprevention of excessive emission from the device. Such a limit is termedutpl. The transmission (tpl′(f)) according to such limitation isdepicted in Table 1.

TABLE 1   ${{tpl}^{\prime}(f)} = \{ \begin{matrix}{utpl} & {{{tpl}(f)} > {utpl}} \\{{tpl}(f)} & {else}\end{matrix} $

According to some embodiments, an upper limit may be imposed on thepower level that is allowed to be dissipated into the load forprevention of damage to the load and/or the device and/or prevention ofexcessive emission from the device or for any other reason. The upperlimit in such a case is termed herein as upl. The limitation is definedin Table 2, wherein gl(f) denotes the amount of power to be dissipatedinto the load at each frequency regardless of upl, and gl′(f) denotesthe amount of power to be dissipated into the load at each frequencywhen taking upl into account.

TABLE 2   ${{gl}^{\prime}(f)} = \{ \begin{matrix}{upl} & {{{gl}(f)} > {upl}} \\{{gl}(f)} & {else}\end{matrix} $Finally, at times two or more of upl, utpl and bpl may be used.Exemplary Method for Selecting FTPS:

dr(f), being the dissipation ratio at a given frequency, has potentialvalues between 0 and 1, and may be computed as shown in Equation 1,based on the measured power and using measured S-parameters, as known inthe art.

${{dr}_{j}(f)} = {\frac{{P_{{incident},{watt}}^{i}(f)} - {\sum\limits_{i}^{\;}{P_{{returned},{watt}}^{i}(f)}}}{P_{{incident},{watt}}^{i}(f)} = {1\frac{\sum\limits_{i}^{\;}{P_{{returned},{watt}}^{i}(f)}}{P_{{incident},{watt}}^{i}(f)}}}$

The maximum power that can be dissipated in the load at each frequency(depicted as ep_(j)(f)) is calculated as follows, given thatP_(maximum,j,watt) is a maximum power available from the amplifier ateach frequency.ep _(j)(f)=dr _(j)(f)P _(maximum,j,watt)(f)

In any given dissipation cycle, gl(f) denotes the power to be dissipatedinto the load at each frequency. dpl(f) is defined as the amount ofpower that is desired to be dissipated in the load at a given frequencyand the dissipation is therefore as described in table 3.

TABLE 3   ${{gl}(f)} = \{ \begin{matrix}{{dpl}(f)} & {{{dpl}(f)} \leq {{ep}(f)}} \\{{ep}(f)} & {else}\end{matrix} $

Note: gl(f) (and ep(f) and dpl(f)) is a powers that are to be dissipatedinto the load; the power to be transmitted by the device at eachfrequency (tpl(f)) is a function of gl(f) and dr(f) as described intable 4.

TABLE 4   ${{tpl}(f)} = \frac{{gl}(f)}{{dr}(f)}$

In cases where a bpl is applied such that transmitted is prevented fortpl(f) values lower than bpl, the actual transmission (ttl′(f)) istherefore as described in table 5.

TABLE 5   ${{tpl}^{\prime}(f)} = \{ \begin{matrix}0 & {{{tpl}(f)} < {bpl}} \\{{tpl}(f)} & {else}\end{matrix} $Transmission Time Calculation:

In some exemplary embodiments of the invention, a basic time step ischosen (hereinafter termed bts (e.g., 10 nsec)). The basic time step isnormally a feature of the controller that controls the time fortransmission of each frequency and defines the maximal resolution intime units between transmitted frequencies. ttd(f) is a numerical value,which defines the time needed to transmit tpl(f), as measured in btsunits. ttd(f) may be calculated as follows:

${{ttd}(f)} = \frac{{tpl}^{\prime}(f)}{{{ep}(f)}/{dr}}$

Accordingly, the minimal transmission time may be calculated as afunction of ttd(f) and bts. At times, it may be desired to impose acycle time that would transmit at least a meaningful amount of energy,or that the cycle time would not be very short for any other reason.Therefore, a time stretch constant (tsc) may be introduced to increasethe cycle time above the aforementioned minimum, thereby calculating theactual transmission time for each frequency (att(f)) as follows:att(f)=ttd(f)*bts*tsc

tsc may be used to increase/decrease a cycle duration. This may be afixed value for a device or different fixed values may be set fordifferent operation protocols of the device or based on characteristicsof the load, or adjusted from time to time during an operation cycle(e.g. based on limitations for a total amount of energy is transmittedper cycle), etc. In fact, at times, increasing the value of tsc may beused in order to transmit low dpl(D values, which may increase theoverall duration of the energy transmission process, but might providemore exactly the desired dissipation pattern.

It should be noted, that a given total amount of transmission time(att(f)) is assigned to each frequency so that this period is notnecessarily transmitted continuously. Rather, a transmission cycle maybe broken down to a plurality of cycles, wherein some or all of thetransmitted frequencies are transmitted for periods smaller than att(f)whilst the total transmission time for each frequency is maintained asatt(f).

Demonstration of Time Reduction:

The exemplary description is based on two transmitted frequencies f₁ andf₂ and a maximum transmittal power of a device P_(maximum)=P₁>P₂.According to a selected power transfer protocol based on adjusting thepower transmitted, P₁ is transmitted at f₁ and P₂ at f₂, each for afixed period of time t. In such case, the total time used to transmit E₁and E₂ is 2t.E ₁ =P ₁ tE ₂ =P ₂ tt _(total)=2t

According to a selected power transfer protocol based on adjusting thetime during which energy is transmitted, P_(maximum) is transmitted atboth f₁ and f₂. In such case, the total time used to transmit E₁ and E₂is calculated as follows:E ₁ =P _(maximum) t ₁ =P ₁ tE ₂ =P _(maximum) t ₂ =P ₂ t

Since P_(maximum)=P₁, t₁ must be equal to t. But since P_(maximum)>P₂,t₂ must be smaller than t:t ₂ =t−δt _(total) =t ₁ +t ₂ =t+(t−δ)=2t−δ<2t

FIG. 3 schematically depicts a device 10 according to an embodiment ofthe present invention. Device 10, as shown, comprises a cavity 11.Cavity 11 as shown is a cylindrical cavity made of a conductor, forexample a metal such as aluminum. However, it should be understood thatthe general methodology of the invention is not limited to anyparticular resonator cavity shape. Cavity 11, or any other cavity madeof a conductor, operates as a resonator for electromagnetic waves havingfrequencies that are above a cutoff frequency (e.g. 500 MHz) which maydepend, among other things, on the geometry of the cavity. Methods ofdetermining a cutoff frequency based on geometry are well known in theart, and may be used.

A load 12 (a/k/a an object) is placed in the cavity, which may be aFaraday cage, optionally on a supporting member 13 (e.g., a microwaveoven plate). In an exemplary embodiment of the invention, cavity 11 mayinclude one or more feeds 14 which may be used for transmitting energyinto the cavity for resonating in the presence of the load in a sequenceof frequencies. The energy is transmitted using any method and meansknown in that art, including, for example, use of a solid stateamplifier. One or more, and at times all, of the feeds 14 can also beused one or more times during operation for obtaining the spectralinformation of the cavity, and/or dissipation information of the load,within a given band of RF frequencies to determine the spectralinformation of the cavity, e.g., dissipation information of the load, asa function of frequency in the working band. This information iscollected and processed by controller 17, as will be detailed below.

Controller 17 may include at least one processor configured to executeinstructions associated with the presently disclosed embodiments. Asused herein, the term “processor” may include an electric circuit thatperforms a logic operation on input or inputs. For example, such aprocessor may include one or more integrated circuits, microchips,microcontrollers, microprocessors, all or part of a central processingunit (CPU), graphics processing unit (GPU), digital signal processors(DSP), field-programmable gate array (FPGA) or other circuit suitablefor executing instructions or performing logic operations.

Cavity 11 may include, or, in some cases define, an energy applicationzone. Such an energy application zone may be any void, location, region,or area where electromagnetic energy may be applied. It may include ahollow, or may be filled or partially filled with liquids, solids,gases, plasma, or combinations thereof. By way of example only, anenergy application zone may include an interior of an enclosure,interior of a partial enclosure, open space, solid, or partial solid,that allows existence, propagation, and/or resonance of electromagneticwaves. For purposes of this disclosure, all such energy applicationzones may be referred to as cavities. An object is considered “in” theenergy application zone if at least a portion of the object is locatedin the zone or if some portion of the object receives deliveredelectromagnetic radiation.

As used herein, the terms radiating element and antenna may broadlyrefer to any structure from which electromagnetic energy may radiateand/or be received, regardless of whether the structure was originallydesigned for the purposes of radiating or receiving energy, andregardless of whether the structure serves any additional function. Forexample, a radiating element or an antenna may include an aperture/slotantenna, or an antenna which includes a plurality of terminalstransmitting in unison, either at the same time or at a controlleddynamic phase difference (e.g. a phased array antenna). Consistent withsome exemplary embodiments, feeds 14 may include an electromagneticenergy transmitter (referred to herein as “a transmitting antenna”) thatfeeds energy into electromagnetic energy application zone, anelectromagnetic energy receiver (referred herein as “a receivingantenna”) that receives energy from the zone, or a combination of both atransmitter and a receiver.

Energy supplied to a transmitting antenna may result in energy emittedby the transmitting antenna (referred to herein as “incident energy”).The incident energy may be delivered to the energy application zone, andmay be in an amount equal to the one that is supplied to the antennas bya source. Of the incident energy, a portion may be dissipated by theobject (referred to herein as “dissipated energy”). Another portion maybe reflected at the transmitting antenna (referred to herein as“reflected energy”). Reflected energy may include, for example, energyreflected back to the transmitting antenna due to mismatch caused by theobject and/or the energy application zone. Reflected energy may alsoinclude energy retained by the port of the transmitting antenna (i.e.,energy that is emitted by the antenna but does not flow into the zone).The rest of the incident energy, other than the reflected energy anddissipated energy, may be transmitted to one or more receiving antennasother than the transmitting antenna (referred to herein as “transmittedenergy.”). Therefore, the incident energy (“I”) supplied to thetransmitting antenna may include all of the dissipated energy (“D”),reflected energy (“R”), and transmitted energy (“T”), the relationshipof which may be represented mathematically as I=D+R+ΣT_(i).

In accordance with certain aspects of the invention, the one or moretransmitting antennas may deliver electromagnetic energy into the energyapplication zone. Energy delivered by a transmitting antenna into thezone (referred to herein as “delivered energy” or “d”) may be theincident energy emitted by the antenna minus the reflected energy at thesame antenna. That is, the delivered energy may be the net energy thatflows from the transmitting antenna to the zone, i.e., d=I−D.Alternatively, the delivered energy may also be represented as the sumof dissipated energy and transmitted energy, i.e., d=R+T.

In an exemplary embodiment of the invention, cavity 11 may also includeone or more sensors 15. These sensors may provide additional informationto controller 17, including, for example, temperature, detected by oneor more IR sensors, optic fibers or electrical sensors, humidity,weight, etc. Another option is use of one or more internal sensorsembedded in or attached to the load (e.g. an optic fiber or a TTT asdisclosed in WO07/096,878).

Alternatively or additionally, cavity 11 may include one or more fieldadjusting elements (FAE) 16. An FAE is any element within the cavitythat may affect its spectral information (or dissipation information orRC spectrum) or the information derivable therefrom. Accordingly, an FAE16 may be for example, any load within cavity 11, including one or moremetal components within the cavity, feed 14, supporting member 13 andeven load 12. The position, orientation, shape and/or temperature of FAE16 are optionally controlled by controller 17. In some embodiments ofthe invention, controller 17 may be configured to perform severalconsecutive sweeps. Each sweep is performed with a different FAEproperty (e.g., changing the position or orientation of one or more FAE)such that a different spectral information (e.g. dissipation informationor RC spectrum) may be deduced. Controller 17 may then select the FAEproperty based on the obtained spectral information. Such sweeps may beperformed before transmitting RF energy into the cavity, and the sweepmay be performed several times during the operation of device 10 inorder to adjust the transmitted powers and frequencies (and at timesalso the FAE property) to changes that occur in the cavity duringoperation.

At times, the FAEs are controlled and/or the load is rotated or moved,so that more useful spectral information (e.g., dissipation informationor RC spectrum) may be acquired for selective irradiation and/or forsetting of radiation parameters such as dpl (and any of other radiationparameters defined herein), for example as described below. Optionallyor alternatively, the load and/or FAEs are periodically manipulatedand/or based on a quality or other property of the acquired spectralinformation. Optionally, the settings are selected which allow a highestdpl(f) to be selected.

An exemplary transfer of information to the controller is depicted bydotted lines. Plain lines depict examples of the control exerted bycontroller 17 (e.g., the power and frequencies to be transmitted by anfeed 14 and/or dictating the property of FAE 16). Theinformation/control may be transmitted by any means known in the art,including wired and wireless communication.

Controller 17 may also be used for regulating the energy per frequencyby varying respective durations during which corresponding frequenciesare transmitted.

FIGS. 4a and 4b depict exemplary graphs representing two examples ofadjusting parameters before performing a duty cycle, in order todissipate the same amount of energy at a plurality of frequencies. FIG.4A represents a power-adjusted method while FIG. 4B represents atime-adjusted method. In this example, the t-adjusted method is onewherein the amount of time allotted per each frequency before isadjusted performing a duty cycle while maintaining a fixed amount ofpower per each transmitted frequency, and the time adjusted method isone wherein the amount of power per each frequency is adjusted beforeperforming duty cycle while maintaining the time allotted per eachfrequency fixed.

The dashed lines in FIG. 4A and in FIG. 4B respectively represent themaximum power that can be dissipated in the load at each frequency(ep(f)). As shown in the figures, the maximum dissipated power (ep(f))is the same in both figures. In both figures, a limiting factor termedmpl is introduced, denoting a maximal power level above whichdissipation is prevented. In FIG. 4A, the time for transmission of eachfrequency is fixed, and the power chosen to be dissipated at eachfrequency is the same, and is selected to be dpl (e.g. based on atradeoff between heating at high power and using a large number offrequencies having an ep(f) that is at least equal to dpl). As can beseen, some frequencies having ep(f)<dpl are not transmitted, and all buta few frequencies are transmitted below their ep(f). In FIG. 4B whichrepresents a time-adjusted method, most of the frequencies aretransmitted at respective ep(f), except those having ep(f)>mpl. The linedenoting dpl in FIG. 4B shows the same dpl line appearing in FIG. 4A andis provided merely for comparison between the two graphs.

FIG. 5 is an exemplary scenario of selecting the frequencies that appearin each cycle, according to embodiments of the present invention. Inthis example the time allotted per each frequency is fixed in each dutycycle and the adjustment is achieved by determining which frequencyappears in which duty cycle. Such an adjustment takes into considerationthe desired percentage of energy transmitted at each frequency. Acertain frequency may appear in all duty cycles to provide a hundredpercent of its maximum energy while another frequency may appear in oneout of a plurality of duty cycles (e.g., 1 in 3) to achieve a portion(one third in the aforementioned example) of its maximum energy output.Increased resolution may be achieved if selecting not to transmit afrequency or transmitting but below its full power for some of thecycles. In box 42, the load is irradiated by UHF or microwave radiation,using a sequence of frequencies in a duty cycle. In box 44, dissipationinformation is obtained from the load. In box 46, energy levels areselected for each frequency that participates in the current duty cyclebased on respective dissipation levels and desired energy dissipationfor the load. In box 48, the duty cycle is modified by varying thefrequencies that take place in the duty cycle. In box 49, the load isirradiated according to the modified duty cycle, which may then befollowed by box 42 of a new round of duty cycle modification. Thedesired energy dissipation is obtained from pre-selected energydissipation information.

In another example, power is provided as multi-frequency pulses, witheach pulse including power in a plurality of frequencies; thefrequencies in each pulse and/or amplitude of the power for a frequencyin a pulse may be selected to apply a desired average power.

Returning to several of the concepts introduced above, it should benoted that, in certain embodiments, at least one processor may beconfigured to determine a value indicative of energy absorbable by theobject at each of a plurality of frequencies or MSEs (The MSE conceptwill be described later in greater detail). This may occur using one ormore lookup tables, by pre-programming the processor or memoryassociated with the processor, and/or by testing an object in an energyapplication zone to determine its absorbable energy characteristics. Oneexemplary way to conduct such a test is through a sweep or scan.

As used herein, the word “sweep” may include, for example, thetransmission over time of more than one frequency or MSE. For example, asweep may include the sequential transmission of multiple frequencies orMSEs in a contiguous frequency or MSE band; the sequential transmissionof multiple frequencies or MSEs in more than one non-contiguousfrequency or MSE band; the sequential transmission of individualnon-contiguous frequencies or MSEs; and/or the transmission ofsynthesized pulses having a desired frequency (or MSE)/power spectralcontent (i.e. a synthesized pulse in time). Thus, during a frequency orMSE sweeping process, the at least one processor may regulate the energysupplied to the at least one antenna to sequentially deliverelectromagnetic energy at various frequencies or MSEs to an energyapplication zone 90, and to receive feedback which serves as anindicator of the energy absorbable by object or load 110, as shown inFIG. 6. While the invention is not limited to any particular measure offeedback indicative of energy absorption in the object, variousexemplary indicative values are discussed below.

During the sweeping process, electromagnetic energy applicationsubsystem 96 may be regulated to receive electromagnetic energyreflected and/or coupled at antenna(s) 102 (including feeds or antennas14, for example), and to communicate the measured energy informationback to subsystem 92 via interface 130, as illustrated in FIG. 6.Subsystem 92, which may include one or more processors, may thendetermine a value indicative of energy absorbable by object 110 at eachof a plurality of frequencies or MSEs based on the received information.Consistent with the presently disclosed embodiments, a value indicativeof the absorbable energy may be a dissipation ratio (referred to hereinas “DR”) associated with each of a plurality of frequencies or MSEs. Asreferred herein, a “dissipation ratio,” also known as “absorptionefficiency” or “power efficiency”, may be defined as a ratio betweenelectromagnetic energy absorbed by object 110 and electromagnetic energysupplied into electromagnetic energy application zone 90.

Energy that may be dissipated or absorbed by an object is referred toherein as “absorbable energy.” Absorbable energy may be an indicator ofthe object's capacity to absorb energy or the ability of the apparatusto cause energy to dissipate in a given object. In some of the presentlydisclosed embodiments, absorbable energy may be calculated as a productof the maximum incident energy supplied to the at least one antenna andthe dissipation ratio. Reflected energy (i.e., the energy not absorbedor transmitted) may, for example, be a value indicative of energyabsorbed by the object or other load. By way of another example, aprocessor might calculate or estimate absorbable energy based on theportion of the incident energy that is reflected and the portion that istransmitted. That estimate or calculation may serve as a valueindicative of absorbed energy.

During a frequency or MSE sweep, for example, the at least one processormay be configured to control a source of electromagnetic energy suchthat energy is sequentially supplied to an object at a series offrequencies or MSEs. The at least one processor may then receive asignal indicative of energy reflected at each frequency or MSE, andoptionally also a signal indicative of the energy transmitted to otherantennas. Using a known amount of incident energy supplied to theantenna and a known amount of energy reflected and/or transmitted (i.e.,thereby indicating an amount absorbed at each frequency or MSE) anabsorbable energy indicator may be calculated or estimated. Or, theprocessor may simply rely on an indicator of reflection as a valueindicative of absorbable energy.

Absorbable energy may also include energy that may be dissipated by thestructures of the energy application zone in which the object islocated. Because absorption in metallic or conducting material (e.g.,the cavity walls or elements within the cavity) is characterized by alarge quality factor (also known as a “Q factor”), such frequencies orMSEs may be identified as being coupled to conducting material, and attimes, a choice may be made not to transmit energy in such sub bands. Inthat case, the amount of electromagnetic energy absorbed in the cavitywalls may be substantially small, and thus, the amount ofelectromagnetic energy absorbed in the object may be substantially equalto the amount of absorbable energy.

In the presently disclosed embodiments, a dissipation ratio may becalculated using the formula:DR=(P _(in) −P _(rf) −P _(cp))/P _(in)where P_(in) represents the electromagnetic energy supplied into zone 90by antennas 102, P_(rf) represents the electromagnetic energyreflected/returned at those antennas that function as transmitters, andP_(cp) represents the electromagnetic energy coupled at those antennasthat function as receivers. DR may be a value between 0 and 1, and, inthe presently disclosed embodiments, may be represented by a percentagenumber.

For example, in a three antenna system including antennas 1, 2, and 3,subsystem 92 may be configured to determine input reflectioncoefficients S11, S22, and S33 and the transfer coefficients S12=S21,S13=S31, S23=S32 based on the measured power information during thesweep. Accordingly, the dissipation ratio DR corresponding to antenna 1may be determined based on these coefficients, according to the formula:DR=1−(IS ₁₁ I ² +IS ₁₂ I ² +IS ₁₃ I ²).

For a particular object 110, the dissipation ratio may change as afunction of the frequency or MSE of the supplied electromagnetic energy.Accordingly, a dissipation ratio spectrum may be generated by plottingthe dissipation ratio associated with each frequency or MSE against therespective frequencies or MSEs. Exemplary dissipation ratio (efficiency)spectrums 210 and 250 are illustrated in FIG. 7 and FIG. 8,respectively. FIG. 7 depicts frequencies and FIG. 8 depicts MSEscorresponding to both high and low dissipation ratios. Both illustratedissipation ratio peaks that are broader than others.

FIG. 8 illustrates a dissipation ratio spectrum 250 over a range ofmodulation space elements (MSEs). The spectrum 250 plots dissipationratios (DR) for a particular range of MSEs. Spectrum 250 may includecertain areas, such as local peak 254, which are higher than thesurrounding areas. Local peak 254 may indicate that a higher percentageof power is dissipated at the corresponding MSE or range of MSEs. Curve225 may represent a desired level of energy dissipation over a pluralityof MSEs. Based on the information included in dissipation ratio spectrum250, the power at which energy is applied and/or the time duration forwhich energy is applied at various MSEs may be determined tosubstantially achieve the desired energy dissipation level 225.

Returning to FIG. 7, curve 210 represents a spectrum of dissipationratio values over a range of frequencies. Using this information, adesired power level can be provided at each of a plurality offrequencies within this range to achieve a desired energy applicationprofile. Curve 220 represents the power level applied over the frequencyband. It can be seen that the power level is substantially inverselyproportional to the dissipation ratio curve 210. In the example shown inFIG. 7, 400 W represents the maximum power available to transmit.

According to another exemplary embodiment, the at least one processormay be configured to regulate subsystem 96 (FIG. 6) for measuring afirst amount of incident energy at a transmitting antenna at a firstfrequency or MSE; measure a second amount of energy reflected at thetransmitting antenna as a result of the first amount of incident energy;measure a third amount of energy transmitted to a receiving antenna as aresult of the first amount of incident energy; and determine thedissipation ratio based on the first amount, the second amount, and thethird amount. By way of example, the at least one processor may beconfigured to measure a first amount of incident energy at a firstantenna 102 which performs as a transmitter at a first frequency or MSE,measure a second amount of energy reflected at first antenna 102 as aresult of the first amount of incident energy, measure a third amount ofenergy transmitted to at least one second antenna 102 which performs asa receiver as a result of the first amount of incident energy, anddetermine the dissipation ratio based on the first amount, the secondamount, and the third amount.

The value indicative of the absorbable energy may further involve themaximum incident energy associated with a power amplifier associatedwith subsystem 96 at the given frequency. As referred herein, a “maximumincident energy” may be defined as the maximal power that may beprovided to the antenna at a given frequency or MSE throughout a givenperiod of time. Thus, one alternative value indicative of absorbableenergy may be the product of the maximum incident energy and thedissipation ratio. These are just two examples of values that may beindicative of absorbable energy which could be used alone or together aspart of control schemes implemented using the processor. Alternativeindicia of absorbable energy may be used, depending on the structureemployed and the application.

In certain embodiments, the processor may also be configured to causeenergy to be supplied to the at least one radiating element in at leasta subset of the plurality of frequencies or MSEs, wherein energytransmitted to the zone at each of the subset of frequencies or MSEs maybe a function of the absorbable energy value at each frequency or MSE.For example, the energy supplied to the at least one antenna 102 at eachof the subset of frequencies or MSEs may be determined as a function ofthe absorbable energy value at each frequency or MSE (e.g., as afunction of a dissipation ratio, maximum incident energy, a combinationof the dissipation ratio and the maximum incident energy, or some otherindicator). In some of the presently disclosed embodiments, this mayoccur as the result of absorbable energy feedback obtained during afrequency or MSE sweep. That is, using this absorbable energyinformation, the at least one processor may adjust energy supplied ateach frequency or MSE such that the energy at a particular frequency orMSE may in some way be a function of an indicator of absorbable energyat that frequency or MSE. The functional correlation may vary dependingupon application. For some applications where absorbable energy isrelatively high, there may be a desire to have the at least oneprocessor implement a function that causes a relatively low supply ofenergy at each of the emitted frequencies or MSEs. This may bedesirable, for example when a more uniform energy distribution profileis desired across object 110.

For other applications, there may be a desire to have the processorimplement a function that causes a relatively high supply of energy.This may be desirable to target specific areas of an object with higherabsorbable energy profiles. For yet other applications, it may bedesirable to customize the amount of energy supplied to a known orsuspected energy absorption profile of the object 110. In still otherapplications, a dynamic algorithm or a look up table can be applied tovary the energy applied as a function of at least absorbable energy andperhaps one or more other variables or characteristics. These are but afew examples of how energy transmitted into the zone at each of thesubset of frequencies or MSEs may be a function of the absorbable energyvalue at each frequency or MSE. The invention is not limited to anyparticular scheme, but rather may encompass any technique forcontrolling the energy supplied by taking into account an indicator ofabsorbable energy.

In certain embodiments, the energy supplied to the at least oneradiating element at each of the subset of frequencies or MSEs may be afunction of the absorbable energy values at the plurality of frequenciesor MSEs other than the frequency or MSE at which energy is supplied. Forexample, in some of the presently disclosed embodiments, the dissipationratios at a range of “neighborhood” frequencies or MSEs around thefrequency or MSE at issue may be used for determining the amount ofenergy to be supplied. In some of the presently disclosed embodiments,the entire working band excluding certain frequencies or MSEs that areassociated with extremely low dissipation ratios (which may beassociated with metallic materials, for example) may be used for thedetermination.

In certain embodiments, the processor may be configured to cause energyto be supplied to the at least one radiating element in at least asubset of the plurality of frequencies or MSEs, wherein energytransmitted to the zone at each of the subset of frequencies or MSEs isinversely related to the absorbable energy value at each frequency orMSE. Such an inverse relationship may involve a general trend—when anindicator of absorbable energy in a particular frequency or MSE subset(i.e., one or more frequencies or MSEs) tends to be relatively high, theactual incident energy at that frequency or MSE subset may be relativelylow. And when an indicator of absorbable energy in a particularfrequency or MSE subset tends to be relatively low, the incident energymay be relatively high.

The inverse relationship may be even more closely correlated. Forexample, in some of the presently disclosed embodiments, the transmittedenergy may be set such that its product with the absorbable energy value(i.e., the absorbable energy by object 110) is substantially constantacross the frequencies or MSEs applied. In either case, a plot oftransmitted energy may generally appear as a reverse image of a valueindicative of absorption (e.g., dissipation ratio or a product of thedissipation ratio and the maximal incident power available at eachtransmitted frequency). For example, FIG. 7 provides a plotted exampleof a dissipation ratio spectrum 210 (dashed line) and a correspondingincident power spectrum 220 (solid line) taken during operation of adevice constructed and operated in accordance with some of the presentlydisclosed embodiments. The plots shown in FIG. 7 were taken with an ovenhaving a maximum incident power of about 400 Watts, wherein a 100 grchunk of minced beef was placed. A range of frequencies between 800 MHzand 1 GHz was swept, and energy was supplied based on the sweep, suchthat essentially uniform dissipation of energy will be affected in thechunk of beef.

In certain embodiments, the at least one processor may be configured toadjust energy supplied such that when the energy supplied is plottedagainst an absorbable energy value over a range of frequencies or MSEs,the two plots tend to mirror each other. In some of the presentlydisclosed embodiments, the two plots may be mirror images of each other.In some of the presently disclosed embodiments, the plots may notexactly mirror each other, but rather, have generally opposite slopedirections, i.e., when the value corresponding to a particular frequencyor MSE in one plot is relatively high, the value corresponding to theparticular frequency or MSE in the other plot may be relatively low. Forexample, as shown in FIG. 7, the relationship between the plot oftransmitted energy (e.g., incident power spectrum 220) and the plot ofthe absorbable energy values (e.g., dissipation ratio spectrum 210) maybe compared such that when the transmitted energy curve is increasing,over at least a section of the curve, the absorbable energy curve willbe decreasing over the same section. Additionally, when the absorbableenergy curve is increasing, over at least a section of the curve, thetransmitted energy curve will be decreasing over the same section. Forexample, in FIG. 7, incident power spectrum 220 increases over thefrequency range of 900 Hz-920 Hz, while dissipation ratio spectrum 210decreases over that frequency range. At times, the curve of transmittedenergy might reach a maximum value, above which it may not be increased,in which case a plateau (or almost plateau) may be observed in thetransmission curve, irrespective of the absorbable energy curve in thatsection. For example, in FIG. 7, when the incident power reaches themaximum value of 400 W, the incident power stays substantially constantregardless of the variations in the dissipation ratio.

Some exemplary schemes can lead to more spatially uniform energyabsorption in the object 110. As used herein, “spatial uniformity”refers to a condition where the energy absorption (i.e., dissipatedenergy) across the object or a portion (e.g., a selected portion) of theobject that is targeted for energy application is substantiallyconstant. The energy absorption is considered “substantially constant”if the variation of the dissipated energy at different locations of theobject is lower than a threshold value. For instance, a deviation may becalculated based on the distribution of the dissipated energy, and theabsorbable energy is considered “substantially constant” if thedeviation is less than 50%. Because in many cases spatially uniformenergy absorption may result in spatially uniform temperature increase,consistent with some of the presently disclosed embodiments, “spatialuniformity” may also refer to a condition where the temperature increaseacross the object or a portion of the object that is targeted for energyapplication is substantially constant. The temperature increase may bemeasured by a sensing device, such as a temperature sensor in zone 90.

In order to achieve approximate substantially constant energy absorptionin an object or a portion of an object, controller 101 may be configuredto hold substantially constant the amount of time at which energy issupplied to antennas 102 at each frequency or MSE, while varying theamount of power supplied at each frequency or MSE as a function of theabsorbable energy value.

In certain situations, when the absorbable energy value is below apredetermined threshold for a particular frequency, frequencies, MSE orMSEs, it may not be possible to achieve uniformity of absorption at eachfrequency or MSE. In such instances, consistent with some of thepresently disclosed embodiments, controller 101 may be configured tocause the energy to be supplied to the antenna for that particularfrequency, frequencies MSE or MSEs a power level substantially equal toa maximum power level of the device. Alternatively, consistent with someother embodiments, controller 101 may be configured to cause theamplifier to supply no energy at all at a particular frequency,frequencies, MSE or MSEs. At times, a decision may be made to supplyenergy at a power level substantially equal to a maximum power level ofthe amplifier only if the amplifier may supply to the object at least athreshold percentage of energy as compared with the uniform transmittedenergy level (e.g. 50% or more or even 80% or more). At times, adecision may be made to supply energy at a power level substantiallyequal to a maximum power level of the amplifier only if the reflectedenergy is below a predetermined threshold, in order, for example, toprotect the apparatus from absorbing excessive power. For example, thedecision may be made based on the temperature of a dummy load into whichreflected energy is introduced, or a temperature difference between thedummy load and the environment. The at least one processor mayaccordingly be configured to control the reflected energy or theabsorbed energy by a dummy load. Similarly, if the absorbable energyvalue exceeds a predetermined threshold, the controller 101 may beconfigured to cause the antenna to supply energy at a power level lessthan a maximum power level of the antenna.

In an alternative scheme, uniform absorption may be achieved by varyingthe duration of energy delivery while maintaining the power applied at asubstantially constant level. In other words, for frequencies exhibitinglower absorbable energy values, the duration of energy application maybe longer than for frequencies or MSEs exhibiting higher absorptionvalues. In this manner, an amount of power supplied at multiplefrequencies or MSEs may be substantially constant, while an amount oftime at which energy is supplied varies, depending on an absorbableenergy value at the particular frequency or MSE.

In certain embodiments, the at least one antenna may include a pluralityof antennas, and the at least one processor may be configured to causeenergy to be supplied to the plurality of antennas using waves havingdistinct phases. For example, antenna 102 may be a phased array antennaincluding a plurality of antennas forming an array. Energy may besupplied to each antenna with electromagnetic waves at a differentphase. The phases may be regulated to match the geometric structure ofthe phased array. In some of the presently disclosed embodiments, the atleast one processor may be configured to control the phase of eachantenna dynamically and independently. When a phased array antenna isused, the energy supplied to the antenna may be a sum of the energysupplied to each of the antennas in the array.

Because absorbable energy can change based on a host of factorsincluding object temperature, depending on application, it may bebeneficial to regularly update absorbable energy values and thereafteradjust energy application based on the updated absorption values. Theseupdates can occur multiple times a second, or can occur every fewseconds or longer, depending on application. As a general principle,more frequent updates may increase the uniformity of energy absorption.

In accordance with the some of the presently disclosed embodiments, acontroller may be configured to adjust energy supplied from the antennaas a function of the frequency at which the energy is supplied. Forexample, regardless of whether a sweep or some other active indicator ofenergy absorption is employed, certain frequencies or MSEs may betargeted or avoided for energy application. That is, there may befrequencies or MSEs that the controller 101 avoids altogether, such aswhere the absorption level falls below a predetermined threshold. Forexample, metals tend to be poor absorbers of electromagnetic energy, andtherefore certain frequencies or MSEs associated with metals willexhibit low absorption indicator values. In such instances the metalsmay fit a known profile, and associated frequencies may be avoided. Or,an absorption indicator value may be dynamically determined, and when itis below a predetermined threshold, controller 101 may prevent anantenna 102 from thereafter supplying electromagnetic energy at suchfrequencies. Alternatively, if it is desirable to apply energy to onlyportions of an object, energy can be targeted to those portions ifassociated frequency or MSE thresholds are either known or dynamicallydetermined. In accordance with another aspect of the invention, the atleast one processor may be configured to determine a desired energyabsorption level at each of a plurality of frequencies or MSEs andadjust energy supplied from the antenna at each frequency or MSE inorder to target the desired energy absorption level at each frequency orMSE. For example as discussed earlier, the controller 101 may beconfigured to target a desired energy absorption level at each frequencyor MSE in attempt to achieve or approximate substantially uniform energyabsorption across a range of frequencies or MSEs. Alternatively, thecontroller 101 may be configured to target an energy absorption profileacross the object 110, which is calculated to avoid uniform energyabsorption, or to achieve substantially uniform absorption in only aportion of the object 110.

Modulation Space (MS) and Modulation Space Elements (MSES)

As described above, some of the presently disclosed embodiments may beconfigured to achieve a desired heating pattern in a load. Such a loadmay include multiple objects, one or more different phases of amaterial, and/or different material compositions. For example, byscanning a load over a range of frequencies or MSEs, a dissipation ratiocan be determined for each frequency. Using the dissipation ratioinformation, the controller 101 may be configured to target a desiredenergy absorption level at each frequency (or MSE). In one exemplaryembodiment, the level of power supplied at each MSE can be controlledsuch that lower power levels are supplied at MSEs that exhibit highdissipation ratios and higher power levels can be supplied at MSEs thatexhibit low dissipation ratios. Controller 101 can also vary the amountof time during which a fixed power is supplied at a particularfrequency. For example, a certain power level may be applied over arelatively short period of time at MSEs that exhibit high dissipationratios, and the same power level may be applied over a longer period oftime at MSEs that exhibit lower dissipation ratios. As mentioned above,the power level and time durations can also both be controlled toachieve a desired energy delivery profile. For example, both a lowerpower level and a shorter application time may be used at MSEs with highdissipation ratios, and both a high power level and a longer applicationtime may be used at MSEs having lower dissipation ratios. Suchembodiments may achieve or approximate substantially uniform energyabsorption across a range of frequencies, and, in certain exemplaryembodiments, the load may be heated uniformly or according to anotherdesired heating profile.

The presently disclosed embodiments, however, are not limited to theconcept of frequency sweeping and applying power (either fixed orvariable) during varying time durations at frequencies within the sweep.Rather, energy delivery consistent with the presently disclosedembodiments may be accomplished more broadly by controlling anyparameters that have the potential for affecting energy delivery to theload or a portion of the load. Frequency is merely one example of aparameter that can be used to affect energy absorption by the load or aportion of the load.

Electromagnetic waves in the energy application zone may exhibit acertain field pattern. A “field pattern” may refer to an electromagneticfield configuration characterized by, for example, the amplitude ofelectric field intensity distribution in the energy application zone. Ingeneral, electromagnetic field intensity may be time varying andspatially dependent. That is, not only may the field intensity differ atdifferent spatial locations, but for a given location in space, thefield intensity can vary in time or may oscillate, often in a sinusoidalfashion. Therefore, at different spatial locations, the fieldintensities may not reach their maximum values (i.e., their maximumamplitude values) at the same time. Because the field intensityamplitude at a given location can reveal information regarding theelectromagnetic field, such as electromagnetic power density and energytransfer capability, the field pattern referred to herein may include aprofile representing the amplitude of field intensity at one or morespatial locations. Such a field intensity amplitude profile may be thesame as or different from a snapshot of the instant field intensitydistribution at a given time in the zone. As used herein, the term“amplitude” is interchangeable with “magnitude.”

A field pattern may be excited by applying electromagnetic energy to theenergy application zone. As used herein, the term “excited” isinterchangeable with “generated,” “created,” and “applied.” In general,a field pattern in an energy application zone may be uneven (i.e.,non-uniform). That is, the field pattern may include areas withrelatively high amplitudes of field intensity and other areas withrelatively low amplitudes of field intensity. The rate of energytransfer may depend upon the amplitude of field intensity. For example,energy transfer may occur faster at areas with higher amplitude of fieldintensity than in areas with lower amplitude of field intensity. As usedherein, the term “energy transfer” is interchangeable with “energydelivery.”

The apparatus of FIG. 3 may be configured to control a distribution andintensity of high amplitude electromagnetic field (maxima and minima)and low amplitude electromagnetic field in the energy application zone,thus delivering differing target amounts of energy to any two (or more)given regions in the application zone. The energy application may be amodal cavity. As used herein, a “modal cavity” refers to a cavity thatsatisfies a “modal condition.” Modal condition refers to therelationship between the largest resonant wavelength supported by theenergy application zone and the wavelength of the deliveredelectromagnetic energy supplied by the source. If the wavelength of thedelivered electromagnetic energy supplied by the source is greater thanabout one quarter of the largest resonant wavelength supported by theenergy application zone, the modal condition is met. The control ofdistribution and intensity of electromagnetic field in the energyapplication zone can occur through the selection of “MSEs” (as describedlater). Choices of MSE selection may impact how energy is distributed inregions of the energy application zone. When the modal condition is notmet, it may be more difficult to achieve a desired energy applicationdistribution through the control of MSEs.

The term “modulation space” or “MS” is used to collectively refer to allthe parameters that may affect a field pattern in the energy applicationzone and all combinations thereof. In some embodiments, the “MS” mayinclude all possible components that may be used and their potentialsettings (either absolute or relative to others) and adjustableparameters associated with the components. For example, the “MS” mayinclude a plurality of variable parameters, the number of antennas,their positioning and/or orientation (if modifiable), the useablebandwidth, a set of all useable frequencies and any combinationsthereof, power settings (e.g. relative power delivered at the same timeto two or more irradiating feeds), time settings, phases, etc.

Examples of energy application zone-related aspects of the modulationspace may include the dimensions and shape of the energy applicationzone and the materials from which the energy application zone isconstructed. Examples of energy source-related aspects of the modulationspace may include amplitude, frequency, and phase of energy delivery.Examples of radiating element-related aspects of the modulation spacemay include the type, number, size, shape, configuration, orientationand placement of antenna-like structures.

Each variable parameter associated with the MS is referred to as an MSdimension. By way of example, FIG. 10 illustrates a three dimensionalmodulation space 1000, with three dimensions designated as frequency(F), phase (φ), and amplitude (A) (e.g., an amplitude difference betweentwo or more feeds used together to provide energy to a givenelectromagnetic field of a given MSE). That is, in MS 1000, any offrequency, phase, and amplitude of the electromagnetic waves may bemodulated during energy delivery, while all the other parameters may bepredetermined and fixed during energy delivery. An MS may be onedimensional where only one parameter is varied during the energydelivery. An MS may also be higher-dimensional such that more than oneparameter is varied.

The term “modulation space element” or “MSE,” may refer to a specificset of values of the variable parameters in MS. Therefore, the MS mayalso be considered to be a collection of all possible MSEs. For example,two MSEs may differ one from another in the relative amplitudes of theenergy being supplied to a plurality of radiating elements. For example,FIG. 10 shows an MSE 1001 in the three-dimensional MS 1000. MSE 1001 mayhave a specific frequency F(i), a specific phase φ(i), and a specificamplitude A(i). If even one of these MSE variables changes, then the newset defines another MSE. For example, (3 GHz, 30°, 12 V) and (3 GHz,60°, 12 V) are two different MSEs, although only the phase componentchanges. In some embodiments, sequentially swept MSEs may notnecessarily be related to each other. Rather, their MSE variables maydiffer significantly from MSE to MSE (or may be logically related). Insome embodiments, the MSE variables differ significantly from MSE toMSE, possibly with no logical relation between them, however in theaggregate, a group of working MSEs may achieve a desired energyapplication goal.

Differing combinations of these MS parameters may lead to differingfield patterns across the energy application zone and, in turn,differing energy distribution patterns in the object. A plurality ofMSEs that can be executed sequentially or simultaneously to excite aparticular field pattern in the energy application zone may becollectively referred to as an “energy delivery scheme.” For example, anenergy delivery scheme may consist of three MSEs (F₍₁₎, φ₍₁₎, A₍₁₎),(F₍₂₎, φ₍₂₎, A₍₂₎), (F₍₃₎, φ₍₃₎, A₍₃₎). The energy delivery scheme maycomprise additional non MSE parameters, such as the time during whicheach MSE is applied or the power delivered at each MSE. Since there area virtually infinite number of MSEs, there are a virtually infinitenumber of different energy delivery schemes, resulting in virtuallyinfinite number of differing field patterns in any given energyapplication zone (although different MSEs may at times cause highlysimilar or even identical field patterns). Of course, the number ofdiffering energy deliver schemes may be, in part, a function of thenumber of MSEs that are available. The invention, in its broadest sense,is not limited to any particular number of MSEs or MSE combinations.Rather, the number of options that may be employed could be as few astwo or as many as the designer desires, depending on factors such asintended use, level of desired control, hardware or software resolutionand cost.

As noted above, an apparatus or method of the invention may involve theuse of a processor for executing instructions or performing logicoperations. The instructions executed by the processor may, for example,be pre-loaded into the processor or may be stored in a separate memoryunit such as a RAM, a ROM, a hard disk, an optical disk, a magneticmedium, a flash memory, other permanent, fixed, or volatile memory, orany other mechanism capable of providing instructions to the processor.The processor(s) may be customized for a particular use, or can beconfigured for general-purpose use and perform different functions byexecuting different software.

If more than one processor is employed, all may be of similarconstruction, or they may be of differing constructions electricallyconnected or disconnected from each other. They may be separate circuitsor integrated in a single circuit. When more than one processor is used,they may be configured to operate independently or collaboratively. Theymay be coupled electrically, magnetically, optically, acoustically,mechanically, wirelessly or in any other way permitting at least onesignal to be communicated between them.

A single or multiple processors may be provided for the sole purpose ofregulating the source. Alternatively, a single or multiple processorsmay be provided with the function of regulating the source in additionto providing other functions. For example, the same processor(s) used toregulate the source may also be integrated into a control circuit thatprovides additional control functions to components other than thesource.

In accordance with some embodiments of the invention, at least oneprocessor may be configured to regulate the source in order to deliver afirst predetermined amount of energy to a first predetermined region anda second predetermined amount of energy to a second predetermined regionin the energy application zone, wherein the first predetermined amountof energy is different from the second predetermined amount of energy.For example, field patterns may be selected having known areas with highamplitude of electromagnetic field intensity (hot spots). Thus, byaligning a hot spot with a region in an energy application zone, apredetermined field pattern may be chosen to deliver a firstpredetermined amount of energy to a first predetermined region. Whenanother field pattern is chosen having a differing hot spot, that secondfield pattern may result in delivery of a second predetermined amount ofenergy to a second predetermined region. And as also described later,differing MSEs and/or combinations of MSEs may be chosen in order todeliver differing predetermined amounts of energy to differingpredetermined regions. In either instance, control of the amount ofenergy applied may be achieved through either the processor's selectionof particular field patterns or MSEs, and/or control of, for example,power level (e.g. a total power provided for a given MSE), a duration oftime that power is applied during a particular condition, orcombinations of the above. The processor may make such selections inorder to achieve a desired energy application profile.

The term “region” may include any portion of an energy application zone,such as a cell, sub-volume, sub-division, discrete sub-space, or anysub-set of the energy application zone, regardless of how that subset isdiscretized. In one particular example, the energy application zone mayinclude two regions. In another example, the energy application zone mayinclude more than two regions. The regions may or may not overlap witheach other, and the size of each region may or may not be the same.

The at least one processor may also be configured to predetermine thelocations of the first region and the second region. This may occur, forexample, through reflective feedback from the energy application zone,providing information about a location of an object in the zone. Inother embodiments, this might be achieved through imaging. In someembodiments, the regions may correspond to different portions of theobject, and differing targeted amounts of electromagnetic energy may bedelivered to these different portions of the object. The amount ofenergy actually dissipated in each region may depend on the fieldintensity at that region and the absorption characteristics of thecorresponding portion of the object at that particular region. In yetother embodiments, the predetermined locations may be a function ofknown geometry of a field pattern without reference to an object in theenergy application zone. In some embodiments, locations of the firstregion and the second region may also be predetermined by a user or adevice other than the at least one processor.

Two regions may be located adjacent to each other in the energyapplication zone. For example, the energy application zone may include aregion occupied by an object or a portion of an object, and anotherregion defining an area distinct from the area of the object. In thiscase, these two regions may be adjacent to each other and separated by aboundary. For example, the first region may be within the cup of soupbeing heated, and the second region may be outside of the cup of thesoup. In another example, the energy application zone may include tworegions that have different energy absorption characteristics within theobject. For example, the first region may contain mostly water at thetop layer of the soup, and the second region may contain mostly potatoesand/or meats towards the bottom layer of the soup. In another example,the first region may contain a material of a particular phase (e.g.,liquid water), and the second region may contain the same material, butof a different phase (e.g., solid ice). Because of their differingenergy absorption characteristics, it may be beneficial to excite fieldpatterns with differing electrical field intensities at these tworegions. Based on the difference in the local field intensities and theenergy absorption characteristics of the two regions, the dissipatedenergy in each of the regions may be predetermined. Accordingly, thedissipated energy may be made substantially equal or different, asdesired, across differing regions in the object, by selecting andcontrolling MSEs for constructing a suitable energy deliver scheme fordelivering the energy.

MSE selection may impact how energy is distributed in regions of theenergy application zone. In order to deliver differing targeted amountsof electromagnetic energy to differing predetermined regions in theenergy application zone, the processor may control one or more MSEs inorder to achieve a field pattern that targets energy to a specificpredetermined region in the energy application zone. The selection ofMSEs that result in standing waves may provide an added measure ofcontrol since standing waves tend to exhibit predictable and distinctlydefined “high-intensity regions”(hot spots) and “low-intensity regions”(cold spots), as described earlier, where the a high-intensity regionmay exhibit an energy concentration that is readily distinguishable froma low-intensity region. It is to be understood that the term “cold spot”does not necessarily require a complete absence of applied energy.Rather, it may also refer to areas of diminished intensity relative tothe hot spots. That is, in the high-intensity regions, the amplitude offield intensity is higher than the amplitude of field intensity in thelow-intensity regions. Therefore, the power density in thehigh-intensity region is higher than the power density in thelow-intensity region. The power density and field intensity of a spatiallocation are related to the capability of delivering electromagneticenergy to an object placed in that location. And therefore, the energydelivery or transfer rate is higher in a high-intensity region than thatin a low-intensity region. In other words, the energy delivery ortransfer may be more effective in a high-intensity region. Thus, bycontrolling the high-intensity regions and/or low intensity regions inthe energy application zone, the processor may control the energydelivery to a specific spatial location. Such control of high- andlow-intensity regions may be achieved by control MSEs.

Controllable MSE variables may include one or more of amplitude, phase,and frequency of the transmitted electromagnetic wave; a location,orientation, and configuration of each radiating element; or thecombination of any of these parameters, or other parameters that mayaffect a field pattern. For example, as depicted in FIG. 9, an exemplaryprocessor 1401 may be electrically coupled to various components of asource, such as power supply 1402, modulator 1404, amplifier 1406, andradiating elements 1408. Processor 1401 may be configured to executeinstructions that regulate one or more of these components. For example,processor 1401 may regulate the level of power supplied by power supply1402. Processor 1401 may also regulate the amplification ratio ofamplifier 1406, by switching, for example, the transistors in theamplifier. Alternatively or additionally, processor 1401 may performpulse-width-modulation control of amplifier 1406 such that the amplifieroutputs a desired waveform. Processor 1401 may regulate modulationsperformed by modulator 1404, and may alternatively or additionallyregulate at least one of location, orientation, and configuration ofeach radiating element 1408, such as through an electro-mechanicaldevice. Such an electromechanical device may include a motor or othermovable structure for rotating, pivoting, shifting, sliding or otherwisechanging the orientation or location of one or more of radiatingelements 1408. Processor 1401 may be further configured to regulate anyfield adjusting elements located in the energy application zone, inorder to change the field pattern in the zone. For example, fieldadjusting elements may be configured to selectively direct theelectromagnetic energy from the radiating element, or to simultaneouslymatch a radiating element acting as a transmitter to reduce coupling tothe one or more other radiating elements acting as a receiver.

In another example, when a phase modulator is used, it may be controlledto perform a predetermined sequence of time delays on the AC waveform,such that the phase of the AC waveform is increased by a number ofdegrees (e.g., 10 degrees) for each of a series of time periods.Alternatively, the processor may dynamically and/or adaptively regulatemodulation based on feedback from the energy application zone. Forexample, processor 1401 may be configured to receive an analog ordigital feedback signal from detector 1416, indicating an amount ofelectromagnetic energy received from cavity 1412 (including object1410), and processor 1401 may dynamically determine a time delay at thephase modulator for the next time period based on the received feedbacksignal.

The energy distribution that results from any given combination of MSEsmay be determined, for example, through testing, simulation, oranalytical calculation. Using the testing approach, sensors (e.g., smallantenna) can be placed in an energy application zone, to measure theenergy distribution that results from a given combination of MSEs. Thedistribution can then be stored in, for example, a look-up table. In asimulated approach, a virtual model may be constructed so thatcombinations of MSEs can be tested in a virtual manner. For example, asimulation model of an energy application zone may be performed in acomputer based on a set of MSEs inputted to the computer. A simulationengine such as CST or HFSS may be used to numerically calculate thefield distribution inside the energy application zone. The resultingfield pattern may be visualized using imaging techniques or stored in acomputer as digital data. The correlation between MSE and resultingfield pattern may be established in this manner. This simulated approachcan occur well in advance and the known combinations stored in a look-uptable, or the simulation can be conducted on an as-needed basis duringan energy application operation.

Similarly, as an alternative to testing and simulation, calculations maybe performed based on an analytical model in order to predict energydistribution based on selected combination of MSEs. For example, giventhe shape of an energy application zone with known dimensions, the basicfield pattern corresponding to a given MSE may be calculated fromanalytical equations. This basic field pattern, also known as a “mode,”may then be used to construct a desired field pattern by linearcombinations. As with the simulated approach, the analytical approachmay occur well in advance and the known combinations stored in a look-uptable, or may be conducted on an as-needed basis during an energyapplication operation.

In accordance with some embodiments of the invention, the processor maybe configured to deliver predetermined amounts of energy to at least tworegions in the energy application zone. The energy may be predeterminedbased on known characteristics of the object in the energy applicationzone. For example, in the case of a dedicated oven that repetitivelyheats products sharing the same physical characteristics (e.g.,identical hamburger patties), the processor may be pre-programmed todeliver differing known quantities of energy corresponding at least twoknown field patterns. The processor may apply differing amounts ofenergy depending on the field pattern. That is, the power or duration ofenergy application may be varied as a function of the field patternbeing applied. (i.e., resulting from an MSE). This correlation betweenthe predetermined amounts of energy to be applied and the field patternmay be determined by testing, simulation, or analytical analysis, asdiscussed previously.

The correlation between field pattern and amount of energy delivered mayalso be determined by the energy absorption profile of object 1410. Thatis, object 1410 can be scanned using one or more MSEs, and correspondingdissipation ratios can be determined. Based on the dissipation ratiosand desired energy delivery characteristics, a power level can beselected for each of the scanned MSEs to achieve a desired goal. Forexample, if the goal is to uniformly apply energy across an object'svolume, then the processor might select combinations of MSEs that resultin uniform energy application. If on the other hand, non-uniform energyapplication is desired, then the processor might apply predeterminedamounts of energy with each differing field pattern in order to achievethe desired non-uniformity.

Thus, just as subsets of frequencies may be selected and swept, asdescribed in the frequency sweeping examples above, so too may subsetsof MSEs be selected and swept in order to achieve a desired energyapplication goal. Such a sequential process may be referred to herein as“MSE sweeping.”

MSE sweeping can be used to differentially heat portions or regions ofan object. For example, one or more MSEs may be scanned, and thedissipation characteristics of an object or portion of a load may bedetermined (e.g., dissipation ratios may be determined for the scannedMSEs). Based on the dissipation characteristics of the load, a desiredpower level and time duration may be selected for application at each ofthe scanned MSEs or at a portion of the scanned MSEs. Consistent withsome of the presently disclosed embodiments, the selected power levelmay be fixed or, alternatively, may vary from one MSE to the next.Similarly, the selected time duration for application of power may befixed or, alternatively, may vary from one MSE to the next. In oneexample, MSEs that exhibit large dissipation ratios may be assignedrelatively low power values and/or low time durations for powerapplication, and MSEs that exhibit smaller dissipation ratios may beassigned higher power values and/or longer time durations for powerapplication. Of course, any scheme for assigning power levels and timedurations to the swept MSEs may be employed depending on the particularenergy application goals. MSE sweeping can then be commenced duringwhich the selected power levels are applied for the selected timedurations at the corresponding MSEs. MSE sweeping can continue until theobject has achieved the desired level of heating or a desired thermalprofile.

Periodically, during MSE sweeping, the load may be re-scanned using thesame or different MSEs to obtain an updated set of dissipation ratios.Based on the updated set of dissipation ratios, the power levels andtime durations for power application corresponding to each of the MSEsmay be adjusted. This MSE scanning can occur at any desired ratedepending on the requirements of a particular embodiment. In someembodiments, the MSE scan may be repeated at a rate of about 120 timesper minute. Higher scan rates (e.g., 200/min or 300/min) or lower scanrates (e.g., about 100/min, 20/min, 2/min, 10/thawing time, or 3/thawingtime) may be used. Additionally, the scans can be performednon-periodically. At times, an MSE scan sequence (e.g., one or morescans) may be performed once every 0.5 seconds or once every 5 secondsor at any other rate. Moreover, the period between scans may be definedby the amount of energy to be transmitted into the cavity and/or theamount of energy to be dissipated into the load. For example, after agiven amount of energy (e.g. 10 kJ or less or 1 kJ or less or severalhundreds of joules or even 100 J or less were transmitted or dissipatedinto the load or into a given portion of a load (e.g. by weight such as100 g or by percentage, such as 50% of load)), a new scan may beperformed.

To reiterate and further expand on the principles discussed above, thepresently disclosed embodiments may include an apparatus for applying RFenergy to a load. The apparatus may include at least one processor, asdescribed above. For example, the processor may include an electriccircuit that performs a logic operation on input or inputs. For example,such a processor may include one or more integrated circuits,microchips, microcontrollers, microprocessors, all or part of a centralprocessing unit (CPU), graphics processing unit (GPU), digital signalprocessors (DSP), field-programmable gate array (FPGA) or other circuitsuitable for executing instructions or performing logic operations.

The at least one processor may be configured to receive informationindicative of energy dissipated by the load (a/k/a, object) for each ofa plurality of modulation space elements (MSEs). For example, theinformation received indicative of energy dissipated by the load mayinclude information indicative of an amount of energy absorbed by theload, an amount of energy reflected by the load, or any or any otherdirect or indirect indicator of the load's ability to dissipate energy.In one embodiment, based on the information indicative of energydissipated by the load, the processor may determine a dissipation ratiofor each of the plurality of MSEs (or set of MSEs).

The processor can determine the dissipation ratios for the set of MSEsat any desired rate. In one embodiment, the set of dissipation ratioscorresponding to the set of MSEs may be determined at a rate of at leastabout 120 times per minute. In other embodiments, the set of dissipationratios corresponding to the set of MSEs may be determined at a rate ofless than about 120 times per minute. The rate may depend on the natureof the object, the nature of the MSEs, the physical characteristics ofthe system, and the desired result to be achieved. By way of exampleonly, in some instances a rate of more than five times per second may bedesirable. In other instances a rate of less than twice per second maybe desirable.

The processor may also be configured to associate each of the pluralityof MSEs (each being associated with a field pattern in an energyapplication zone) with a corresponding time duration of powerapplication, based on the received information. As used herein, a timeduration of power application may refer to a length of time during whicha particular power is applied to the load. The processor may be furtherconfigured to associate each of the plurality of modulation spaceelements with a power level value corresponding to the time duration ofpower application associated with the same modulation space element. Theamount of energy available for delivery to the load depends on the powerlevel and the amount of time the power is applied to the load.

The processor may be further configured to regulate energy applied tothe load such that during a sweep of the plurality of MSEs, power isapplied to the load at the corresponding power level value and/or at thecorresponding time duration of power application. For example, asdescribed above, MSEs that exhibit higher dissipation ratios may receivepower at a level lower and/or for a shorter time than other MSEs thatexhibit lower dissipation ratios. Of course any power level within anavailable range and any desired time duration of power application maybe assigned to any MSE according to the requirements or energy deliverygoals of a particular intended use.

As described above, each of the plurality of MSEs may be defined byvalues for any of a plurality of parameters that may affect energydelivery to a load. In one embodiment, the plurality of MSEs may bedefined by values for frequency, phase, and amplitude and optionally forother dimensions. In other embodiments, the MSEs may be one dimensionalsuch that only one parameter varies and any others remain constant. Forexample, a set of one dimensional MSEs may differ from each other inonly one of frequency, phase and amplitude. In certain embodiments, thefrequency values may vary among a plurality of MSEs, while values forother parameters, such as phase and/or amplitude remain constant.

The disclosed embodiments may also include a cavity for receiving theload and at least one radiating element for directing EM energy to theload. Further, the apparatus may include a generator of EM energy forsupplying EM energy to the load via the at least one radiating element.

The power level values and time durations of power applicationassociated with each of a plurality of MSEs can be chosen according toany desired energy delivery scheme. In one embodiment, a time durationof power application corresponding to a first MSE associated with afirst dissipation ratio will be shorter than a time duration of powerapplication corresponding to a second MSE associated with a seconddissipation ratio, where the second dissipation ratio is lower than thefirst dissipation ratio. In other exemplary embodiments, the power levelvalues associated with each of the plurality of modulation spaceelements may be the same.

The presently disclosed embodiments may also include an apparatus forapplying RF energy to a load, where the apparatus includes at least oneprocessor configured to determine a plurality of dissipation ratiosassociated with the load. Based on the plurality of dissipation ratios,the processor may be configured to set frequency/power/time triplets (asdescribed in detail above). The processor may also be configured toregulate application of the frequency/power/time triplets to applyenergy to the load.

In the presently disclosed embodiments, the processor may be configuredto set the MSE/power/time triplets such that an MSE associated with afirst dissipation ratio is assigned a power level lower than a secondMSE associated with a second dissipation ratio, when the firstdissipation ratio is higher than the second dissipation ratio. Theprocessor may also be configured to set the MSE/power/time triplets suchthat an MSE associated with a first dissipation ratio will be assigned atime shorter than a second MSE associated with a second dissipationratio, when the first dissipation ratio is higher than the seconddissipation ratio.

While the forgoing paragraphs describe embodiments of the invention inconnection with dissipation ratios, other embodiments of the inventionmay apply similar principles using indicators other than dissipationratios. For example, indicators of energy reflected to the feed from theenergy application zone may be employed as an alternative, as may be anyother direct, indirect, or inverse indicator of energy absorbability.

Exemplary Application

In the following examples the device used was a 900 Watts device with aworking band at 800-1000 MHz, constructed and operated essentiallyaccording to an embodiment of above-mentioned WO07/096,878 ('878);

1. Warming Algorithm

Tap water (500 gr) was heated by a protocol suitable for providingessentially the same amount of energy to all portions of the load. Atotal of 60 kJ was transmitted to the load (water and the bowl in whichthe water was held) in each experiment.

In a first warming experiment, different amounts of energy weretransmitted at different frequencies by transmitting each frequency forthe same fixed period of time, while varying the period of transmission,according to an embodiment of '878. In this example, the water heatedfrom ca. 22° C. to ca. 38° C. (an increase of 16° C.) in 2:25 minutes.

In a second warming experiment, different amounts of energy weretransmitted at different frequencies by transmitting each frequency atthe maximum available power and varying the time of transmission,according to an embodiment of the present invention. The water washeated from ca. 21° C. to ca. 38° C. (an increase of 17° C.) in 1:58minutes (ca. 80% of the time needed for the first warming experiment).

The difference in temperature increase may be attributed, for example,to inaccuracy of the thermometer and/or to slight differences betweenthe bowls which may have led to different absorbance of RF energy.

2. Thawing Algorithm

Frozen chicken breasts (boneless and skinless; bunched together beforefreezing) were taken from a conventional restaurant freezer at ca. −18°C., and were heated using a protocol intended for thawing, wherein adifferent amount of energy is transmitted at different frequencies, inaccordance with an embodiment of U.S. 61/193,248 and a concurrentlyfiled International PCT application.

In a first thawing experiment different amounts of energy weretransmitted at different frequencies by transmitting each frequency forthe same fixed period of time, while varying the period of transmission,according to an embodiment of '878. A 1500 gr bunch of chicken breastswas heated to 0-5° C. (measured at difference sites of the breasts) in36 minutes.

In a second thawing experiment different amounts of energy weretransmitted at different frequencies by transmitting each frequency atthe maximum available power and varying the time of transmission,according to an embodiment of the present invention. A 1715 gr bunch ofchicken breasts was heated to 0-5° C. (measured at difference sites ofthe breasts) in 20 minutes. It was thus observed that in the secondthawing experiment, ca. 56% of time needed for the first thawingexperiment was sufficient to thaw a larger load.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable sub-combination.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives,modifications, and variations will be apparent to those skilled in theart. Accordingly, it is intended to embrace all such alternatives,modifications, and variations that fall within the spirit and broadscope of the appended claims. All publications, patents, and patentapplications mentioned in this specification are herein incorporated intheir entirety by reference into the specification, to the same extentas if each individual publication, patent or patent application wasspecifically and individually indicated to be incorporated herein byreference. In addition, citation or identification of any reference inthis application shall not be construed as an admission that suchreference is available as prior art to the present invention.

What is claimed is:
 1. A method of heating a load in a cavity byirradiating the load using two radiating elements, the methodcomprising: receiving feedback from the cavity indicative of an amountof energy absorbable by the load; after receiving the feedback,determining, based on the received feedback, a plurality of phasedifferences between radiation emitted by the two radiating elements; andirradiating the load using the two radiating elements with radiationcharacterized by each of the determined plurality of phase differences.2. The method of claim 1, wherein irradiating the load using the tworadiating elements with radiation characterized by each of thedetermined phase differences includes sweeping over the determinedplurality of phase differences.
 3. The method of claim 1, wherein:determining the plurality of phase differences includes determining theplurality of phase differences such that feedback from the cavityindicative of energy absorbable by the load associated with each of thedetermined phase differences is above a predetermined level.
 4. Themethod of claim 1, wherein irradiating the load includes controlling anamount of energy applied at each of the plurality of phase differencesbased on the feedback received from the cavity.
 5. The method of claim1, wherein receiving feedback includes: irradiating the load with thetwo radiating elements at multiple phase differences, receiving feedbackindicative of energy absorption in the load in response to theirradiation at each of the multiple phase differences, and determiningvalues indicative of the amount of energy absorbable by the load basedon the feedback at each of the multiple phase differences.
 6. The methodof claim 1, wherein irradiating the load includes irradiating at thedetermined plurality of phase differences for a plurality of non-zerodurations.
 7. The method of claim 5, comprising associating each of thedetermined plurality of phase differences with a respective non-zerotime duration of power application, based on the feedback received atthe respective phase differences.
 8. The method of claim 7, comprisingdetermining the non-zero time duration based on the determined valuesindicative of the amount of energy absorbable by the load for radiationapplied at each of the plurality of phase differences.
 9. The method ofclaim 1, wherein irradiating the load comprises irradiating at thedetermined plurality of phase differences at a plurality of non-zeropower levels.
 10. The method of claim 9, comprising determining theplurality of non-zero power levels based on values indicative of energyabsorbable by the load at each of the determined plurality of phasedifferences.
 11. The method of claim 5, wherein receiving feedbackindicative of energy absorption in the load includes measuring areflected-coupled spectrum (RC spectrum).
 12. The method of claim 1,wherein the feedback indicative of an amount of energy absorbable by theload includes a dissipation ratio.
 13. The method of claim 1, whereinthe feedback indicative of an amount of energy absorbable by the loadincludes dissipation ratio values associated with multiple phasedifferences.
 14. The method of claim 1, wherein the two radiatingelements are configured to transmit in unison.
 15. The method of claim14, wherein the two radiating elements are configured to transmit inunison at a controlled phase difference.
 16. The method of claim 1,wherein determining the plurality of phase differences includesdetermining the plurality of phase differences such that a maximum powerthat can be dissipated in the load at each of the determined phasedifferences exceeds a threshold value.
 17. The method of claim 1,wherein irradiating the load comprises irradiating at a plurality offrequencies.
 18. An apparatus for heating a load in a cavity byirradiating the load using two radiating elements, the apparatuscomprising a controller configured to: receive feedback from the cavityindicative of an amount of energy absorbable by the load; afterreceiving the feedback, determine, based on the received feedback, aplurality of phase differences between radiation emitted by the tworadiating elements; and cause the two radiating elements to irradiatethe load with radiation characterized by each of the determinedplurality of phase differences.
 19. The apparatus of claim 18, whereinthe controller is configured to control the irradiation of the load bysweeping over the determined plurality of phase differences.
 20. Theapparatus of claim 18, wherein the controller is configured to determinethe plurality of phase differences such that feedback from the cavityindicative of energy absorbable by the load associated with each of thedetermined phase differences is above a predetermined level.
 21. Theapparatus of claim 19, wherein the controller is configured to causeapplication of the determined plurality of phase differencessequentially.
 22. The apparatus of claim 18, wherein the controller isconfigured to cause the apparatus to: irradiate the load with the tworadiating elements at multiple phase differences, receive feedbackindicative of energy absorption in the load in response to theirradiation at the multiple phase differences, and determine valuesindicative of the amount of energy absorbable by the load based on thefeedback at each of the multiple phase differences.
 23. The apparatus ofclaim 18, wherein the controller is configured to cause the apparatus toirradiate at the determined plurality of phase differences for aplurality of non-zero durations.
 24. The apparatus of claim 23, whereinthe controller is configured to determine the plurality of non-zerodurations based on values indicative of the amount energy absorbable bythe load for radiation applied at each of multiple phase differences.25. The apparatus of claim 22, wherein the controller is configured tocause the apparatus to irradiate the load at the determined plurality ofphase differences at a plurality of non-zero power levels.
 26. Theapparatus of claim 25, wherein the controller is further configured todetermine the plurality of non-zero power levels based on the valuesindicative of energy absorbable by the load at the determined pluralityof phase differences.
 27. The apparatus of claim 22, wherein thecontroller is configured to receive feedback indicative of energyabsorption in the load by measuring a reflected-coupled spectrum (RCspectrum).
 28. The apparatus of claim 18, wherein the two radiatingelements are configured to transmit in unison.
 29. The apparatus ofclaim 28, wherein the controller is configured to control a phasedifference between the two radiating elements.
 30. The apparatus ofclaim 18, wherein the controller is configured to determine theplurality of phase differences such that a maximum power that can bedissipated in the load at each of the phase differences exceeds athreshold value.
 31. The apparatus of claim 30, wherein the thresholdvalue is substantially the same for all the determined phasedifferences.
 32. The apparatus of claim 18, wherein the controller isconfigured to determine the plurality of phase differences such that atime period required for a predetermined amount of energy to be absorbedin the load at each determined phase differences is shorter than athreshold period.
 33. The apparatus of claim 32, wherein thepredetermined amount of energy is substantially the same for all thedetermined phase differences.
 34. The apparatus of claim 18, furthercomprising the cavity.
 35. The apparatus of claim 18, further comprisingmore than two radiating elements.
 36. The apparatus of claim 18, whereinthe controller is configured to cause the apparatus to irradiate theload at a plurality of frequencies.
 37. The apparatus of claim 18,wherein the controller is configured to associate each of the pluralityof phase differences with a respective time duration of powerapplication, based on the feedback at the respective phase differences.38. An apparatus for heating a load, the apparatus comprising: a cavityfor placing the load therein; two radiating elements configured toirradiate into the cavity electromagnetic waves at multiple phasedifferences between radiation emitted by the two radiating elements; anda controller configured to: receive feedback from the cavity indicativeof an amount of energy absorbable by the load; and after receiving thefeedback, determine, based on the received feedback, a plurality ofphase differences between radiation emitted by the two radiatingelements.